15 Things to Check Before Buying a Second-Hand Phone
A buyer messaged us last year, fairly upset, about an iPhone 14 he’d bought in perfect condition at a good price. Nothing was wrong with it. The screen was clean, the battery read 91%, the seller had been polite and patient. The problem was that it was a US unit — no SIM tray at all, eSIM only — and his network at the time didn’t issue eSIM profiles for that model. A flawless phone he couldn’t put a number into.
That’s the frustrating category. Not scams, not cracked screens, just a check nobody thought to run.
Here are fifteen of them, roughly in the order you’d actually run them.
Before you leave the house (checks 1-4)
Four of these happen over messages, and they eliminate most bad purchases before you’ve spent an hour travelling.
1. How the seller answers a specific question
Send two narrow questions rather than one broad one. Something like: what’s the exact model number in Settings, and has the screen ever been replaced?
A seller with nothing to hide answers both in one message, usually with more detail than you asked for. A seller who answers one and ignores the other has picked which question to avoid, and they’ve just told you which one matters. Vagueness costs nothing to produce, so treat detail as the signal, not friendliness.
Also glance at how long the account has existed and what else it has listed. Five near-identical phones from one “private” seller is a small business, which isn’t automatically bad — but price it and question it like a business rather than like a neighbour clearing out a drawer.
2. The model number and which region it came from
This is the one that caught the buyer above, and it’s the check almost no guide bothers with.
On iPhone, ask for the Model Number from Settings > General > About. The suffix tells you where the unit was sold, and that suffix carries consequences. US models of the iPhone 14 generation and newer ship without a physical SIM tray. Japanese units have a camera shutter sound that cannot be switched off, because Japanese regulation requires it — same in South Korea. Some Middle East and Hong Kong variants carry two physical SIM slots, which is either exactly what you want or completely irrelevant depending on how you use a phone. Apple publishes a model identification reference that maps this out.
Samsung works the same way through its SM- codes. The suffix separates international units from US carrier stock from Korean domestic models, and in some generations it separates chipsets too — the same phone name shipping with different processors depending on the region it was built for. Different chip, different battery behaviour, different modem.
Ask for a photo of the Settings screen showing the model number. Then look up what that specific string means before you agree to meet.
3. Whether the phone supports your network’s bands
Related, but not the same check.
A phone can be perfectly carrier-free and still be poor on your network, because it’s missing the frequency bands your provider leans on. This shows up as a phone that works fine downtown and drops to nothing at your parents’ house. Find the model’s band list on the manufacturer’s specification page — not on a listing, not on a forum — and compare it against what your carrier publishes.
For 5G this matters more than it did for 4G, since the band mix varies sharply between regions.
4. IMEI, matched and cleared
Ask the seller to dial *#06# and send a photo. Cross-check it against Settings and against the SIM tray etching at the meetup, and run it through the blacklist database your carrier or region provides. A flagged IMEI produces a phone that connects to Wi-Fi happily and never registers on a mobile network.
Our step-by-step on running an IMEI check before you pay covers the regional databases and how to read an ambiguous result.
The first two minutes in your hand (checks 5-8)
You’ve met, you’re holding it. This part is physical and fast.
5. Seams, screws, and whether it’s been opened
Run a fingernail slowly around the whole edge where the display meets the frame. Factory assembly is flush. A phone reassembled on a kitchen table almost always has a lip somewhere, or a hairline gap you can catch a nail in, or adhesive that has squeezed out and been trimmed with a blade.
Then look at the two screws beside the charging port with the flashlight from your own phone. Chewed heads, a mismatched screw, or one missing entirely means it’s been inside a repair shop — which is fine if disclosed, and a problem if the listing said untouched.
Any opening also ends the water resistance rating, regardless of what the box promised. IP ratings apply to factory-sealed units, and no manufacturer honours them after a third-party repair.
6. The three-colour screen test
Pull up a plain white image at full brightness. Then solid black. Then solid grey.
White exposes dead pixels, yellowing, and colour temperature mismatch on a replaced panel. Black shows backlight bleed and pressure marks. Grey is the one people skip and the one that finds burn-in — faint ghosts of a status bar, a keyboard, or navigation buttons, invisible on every other background and completely invisible in listing photos.
While you’re there, drag a finger slowly across the whole surface in an S-pattern and watch for the trace breaking. On Samsung, dial *#0*# and you get a hidden service menu with the colour screens and a touch grid built in, along with speaker, receiver, vibration, and sensor tests. It’s the fastest hardware audit available on any phone, and it takes about ninety seconds to work through.
7. Liquid contact indicator and port condition
Pop the SIM tray. Inside the slot there’s a small indicator sticker — white or silver when the phone has stayed dry, pink or red after liquid contact. It’s on iPhones and on a lot of Android models.
Water damage doesn’t always kill a phone. It kills it later, usually through corrosion on a board that has been sitting quietly for eight months. A tripped indicator on a cheap phone is a gamble; on an expensive one it’s a reason to walk.
Then shine a light into the charging port. Compacted lint looks like a solid floor and causes intermittent charging that people mistake for a dead battery. Green or white powder on the pins is corrosion, and that’s a different conversation entirely.
8. Every lens, both mics, both speakers
Test the cameras individually, not by taking one photo. Switch to the ultrawide, then the telephoto, then the front camera, and take a shot with each in both photo and video mode. Cracked glass over a single rear lens produces flare that only appears on that lens, and a listing photo of the back panel won’t show a hairline.
Record a voice memo and play it back — that covers the bottom mic and the main speaker together. Then place a real call to check the earpiece. People discover dead earpieces on day three, after the seller has stopped replying.
The software checks most buyers never run (checks 9-13)
This is where the money is, and it’s all free.
9. Parts and service history
On iPhone, Settings > General > About, scrolled down. Recent iOS versions on the iPhone XR and XS generation onward show a Parts and Service History entry listing replaced components and flagging any that aren’t genuine, properly calibrated Apple parts.
Backup signals for a swapped display: True Tone missing or greyed out under Display & Brightness, Face ID failing to enroll a new face, or auto-brightness behaving strangely. Face ID is the expensive one, since a botched screen repair frequently kills the dot projector for good.
Android gives you no equivalent log on most brands, which pushes you back onto check 5.
10. Battery health, read sceptically
iPhone: Settings > Battery > Battery Health & Charging. Pixel 8 and later: Settings > About phone > Battery information, which shows cycle count and manufacture date. Samsung hides a real diagnostic inside the Samsung Members app under its interactive checks.
The thing to hold onto is that an old, visibly used phone reading exactly 100% is telling you the battery was replaced, and possibly that it was replaced with an aftermarket cell whose controller reports a fixed number rather than a measurement. Ask when, and by whom. We unpack the whole picture in what battery health percentages actually measure.
11. Bootloader, root, and integrity status on Android
Here’s a check that costs nothing and saves people from a phone that can’t do the one thing they bought it for.
If an Android phone’s bootloader has been unlocked — usually to install a custom ROM or to root it — the device fails Google’s Play Integrity attestation. In plain terms: banking apps refuse to open, contactless payment stops working, some streaming services drop to low resolution, and certain apps won’t install at all. Google documents the Play Integrity attestation system if you want the mechanics.
How to check, in order of effort:
- Watch it boot. An unlocked bootloader usually throws a warning screen for a few seconds before the manufacturer logo.
- Open Settings > About phone, tap the build number seven times to enable Developer options, then look at the OEM unlocking toggle. If it’s greyed out and already on, that’s a strong indicator.
- Try to open a banking app or set up a payment card on the spot.
On Samsung specifically, unlocking the bootloader permanently trips the Knox counter, and that can’t be reversed by re-locking. Samsung’s secure features stay disabled for the life of the device. A seller who mentions flashing, ROMs, or rooting isn’t necessarily hiding anything — plenty of enthusiasts do it openly — but the phone is worth less to a normal buyer and should be priced that way.
12. Real storage capacity and what’s left of it
Check Settings > Storage against what the listing advertised. A 256 GB phone reports somewhere in the low 230s as usable, which is normal formatting overhead. A “256 GB” phone reporting 115 GB total is not a formatting quirk.
This matters most at the very cheap end of the market, where refurbished units occasionally get sold with parts and firmware that don’t match their badge.
13. Warranty status and how much software support is left
Two clocks worth knowing about.
For warranty, run the serial or IMEI through the manufacturer. Apple’s coverage lookup reports remaining warranty and support eligibility from the serial number alone, and it also tells you the phone exists as a legitimate Apple unit. Most large Android brands offer a similar IMEI-based warranty check.
For updates, take the launch year and add the manufacturer’s support window. Google commits to seven years of OS and security updates on the Pixel 8 and later; Samsung matches that from the Galaxy S24 onward. Apple doesn’t publish a formal policy, but iPhones have historically kept receiving major iOS releases for around five to six years. Subtract the current year and you have the number that actually matters — how long this phone stays safe to keep a banking app on.
Function tests and the handover (checks 14-15)
14. Charging, wireless charging, biometrics, sensors
Plug in a charger you brought yourself and watch the estimated time. A phone that should fast-charge and instead reports six hours has a port, cable, or board problem. Wiggle the cable gently while it charges; intermittent contact shows up immediately.
If the model supports wireless charging, test it. A failed coil is invisible any other way.
Enroll your own fingerprint and your own face, rather than watching the seller’s work. Under-display sensors degrade, and a sensor that reads the seller’s thumb ninety percent of the time may read yours half the time. Then check the sensors that quietly matter: rotate the phone to test the accelerometer, cover the earpiece during a call to test proximity, and open a maps app to confirm the compass isn’t spinning.
15. Accounts removed, and setup completed in front of you
The last one, and the one that decides whether you own a phone or a paperweight.
On iPhone, the seller must sign out of their Apple Account and erase the device. Activation Lock ties the phone to their credentials, and Apple retired its public lock-status checker years ago, so there is no way to verify this remotely. The only reliable method is watching the erase and then setting the phone up on your own account.
On Android, the Google account has to be removed before the factory reset, not after. Get that order wrong and Factory Reset Protection locks the device to an account you don’t control. Sellers muddle this constantly out of genuine confusion — the outcome is identical either way.
If the phone uses eSIM, confirm the seller’s profile is deleted and that your carrier will issue a new one for that model.
Reach the home screen, on your account, with your SIM registered. That’s the moment you pay. Not before.
The printable version
| # | Check | Where | Red flag |
|---|---|---|---|
| 1 | Seller responsiveness | Messages | Answers one question, ignores the other |
| 2 | Model / region variant | Settings > General > About | eSIM-only unit, unwanted regional quirks |
| 3 | Network bands | Manufacturer spec page | Missing a band your carrier relies on |
| 4 | IMEI | *#06#, Settings, SIM tray | Mismatch, or blacklist hit |
| 5 | Seams and screws | Edges, port screws | Lip, gap, chewed screw heads |
| 6 | Display | White, black, grey at full brightness | Ghosting, dead pixels, colour mismatch |
| 7 | Liquid indicator | Inside SIM slot | Pink or red sticker |
| 8 | Cameras, mics, speakers | Each lens; voice memo; real call | Flare on one lens, dead earpiece |
| 9 | Repair history | iOS: Settings > General > About | Non-genuine parts listed |
| 10 | Battery | Battery Health / Battery information | 100% on an old phone, no explanation |
| 11 | Bootloader and root | Boot screen, Developer options, banking app | Warning screen, tripped Knox |
| 12 | Storage | Settings > Storage | Total far below the advertised size |
| 13 | Warranty and update runway | Manufacturer IMEI lookup | Fewer than two years of updates left |
| 14 | Charging and sensors | Your own charger, your own biometrics | Slow charge, flaky fingerprint reader |
| 15 | Account locks | Full setup at the meetup | Seller wants to erase it “later” |
Screenshot that table before you go. Fifteen items sounds like a lot until you’re doing them, at which point it’s roughly ten minutes.
Common mistakes to avoid
- Running the checks after paying. Half this list has no remedy once money has moved.
- Trusting the listing’s condition grade. Peer-to-peer grading isn’t standardised. Somebody’s honest “excellent” is somebody else’s “a few marks.”
- Testing biometrics with the seller’s finger. It proves the sensor works for them.
- Assuming a phone that isn’t carrier-locked is right for your network. Locking and band support are separate problems with separate solutions.
- Skipping the boot screen on a suspiciously cheap Android. Ten seconds of watching it start up tells you whether contactless payment will ever work.
- Meeting somewhere with no power outlet. You can’t test charging in a park.
- Treating a repaired phone as automatically bad. A genuine screen replacement done properly is a phone with a newer screen. What’s bad is a repair the seller didn’t mention.
FAQ
How long should inspecting a used phone actually take?
About ten minutes for all fifteen checks once you’ve done it a couple of times. The screen tests and the account handover take the longest; everything else is under a minute each.
Is a phone with a replaced screen worth buying?
Yes, if the replacement was genuine and disclosed, and no if the phone shows a non-genuine parts warning and the seller never mentioned it. The practical test on an iPhone is whether True Tone survived and whether Face ID still enrolls — those two failing together usually means a cheap panel and a repair worth negotiating hard against.
What’s the single most-skipped check on this list?
Bootloader status on Android. Buyers find out weeks later, when a banking app refuses to open on a phone that seems otherwise perfect, and by then the seller is long gone.
Can I check any of this remotely before meeting?
Model number, IMEI, blacklist status, warranty, and battery health can all be verified from screenshots the seller sends. Everything physical needs the phone in your hand.
Does ExploreFrag inspect the phones listed on the site?
ExploreFrag connects buyers and sellers directly, so listings come from the individuals selling them. Run this list yourself on every purchase, regardless of how good the listing looks.
Should I still buy from a seller who gets one of these wrong?
Depends which one. A tripped liquid indicator on a cheap phone is a priced risk; a seller who won’t erase the device at the meetup isn’t a risk, it’s a refusal. Treat physical faults as negotiation and handover refusals as an exit.
Take the table above, screenshot it, and use it on the next phone you go to see — even if it’s one you’re already sure about. The check that saves you is never the one you expected to matter.
If you’re still choosing what to look at, our full guide to buying a used phone covers pricing and timing, and you can see what’s currently listed on ExploreFrag to get a feel for real asking prices in your area.
About the author
Emran Ahmed is the founder and CEO of ExploreFrag, a marketplace for buying and selling used phones and accessories across every brand. He built this checklist out of the support messages ExploreFrag receives after sales go sideways, which is why items 2 and 11 are on it at all — both came from buyers who’d done everything else right. He reviews listings most days and has developed a strong opinion about photos taken with the screen off.
Suggested follow-up topics
- iPhone model numbers explained: what LL/A, ZP/A, and J/A actually mean for buyers — region variants, SIM trays, and shutter sounds.
- How to tell if an Android phone has been rooted or has an unlocked bootloader — with the banking-app and Knox implications spelled out.
- Are 5G bands worth checking on a used phone? — matching model variants to carrier coverage by region.
- Water-damaged phones: what the liquid indicator means and when to walk away — corrosion timelines and repair economics.
- How to price a used phone with a fault — turning each item on this checklist into a number you can negotiate with.