You’re standing in a parking lot with a stranger’s phone in your hand and ten minutes to decide. The listing said “mint condition, battery great.” Test it yourself, right there, before money changes hands. This checklist runs in the order that saves the most time: the checks that end the deal come first, the ones that only move the price come last. Every screen, touch, camera, and sensor check opens in the phone’s own browser, so you need nothing but the phone, your SIM, and a charging cable.
Before you meet: ask for three screenshots
A seller who wants the sale will send these in a minute. A seller who won’t has told you something. Ask for the About screen (Settings, General, About on an iPhone; Settings, About phone on Android) with the model and IMEI showing, the battery health screen, and on an iPhone the Parts and Service History block that sits on the same About screen. Run the IMEI through a blacklist checker at home, before you drive anywhere. Keep the battery screenshot so you can compare it to what the phone shows in person. A number that changed between the photo and the meeting means the screenshot came from a different phone.
Deal-breakers first: blacklist, account locks, carrier lock
Some faults end the deal before you check anything else. Dial *#06# to pull up the IMEI and confirm it matches the screenshot and the SIM tray, then run it through a blacklist checker, your carrier’s site or a free IMEI lookup, to confirm it wasn’t reported lost, stolen, or left with an unpaid balance. A blacklisted phone won’t activate on any network, and nothing you test later changes that.
Then confirm the phone is signed out of its last owner. On an iPhone, open Settings, tap the name at the top, and make sure the Apple ID is signed out and Find My is off. On Android, check that no Google account is left on the device. A phone still locked to someone else’s account is a paperweight. Have the seller sign out and run the factory reset in front of you, not “later.” The order matters on Android: a reset done with the Google account still on the phone trips Factory Reset Protection, and the setup screen will ask for the old owner’s password, which you don’t have.
Next, the carrier lock. On an iPhone, the About screen has a Carrier Lock line, and it should read No SIM restrictions. Anything else means the phone is tied to one carrier, and your SIM may never get a signal. Android phones don’t show a lock line, so the SIM test near the end of this list is the only way to know.
One more lock hides on former work phones. On an iPhone, Settings, General, VPN & Device Management should list nothing. An Android phone that says it’s managed by an organization on the setup screen belongs to a company’s fleet. Either way, walk. A management profile can wipe or lock the phone from a desk you’ll never see, and no seller can remove it for you.
Look it over and check for water
Hold the phone to the light and tilt it. Hairline cracks and deep scratches hide until the glare catches them. Check the frame for dents that point to a hard drop. Then look in the charging port and SIM tray for the liquid contact indicator, a small sticker that turns pink or red after water gets in. A phone that took a swim can run for weeks, then quit. Press every button. Lay the phone face down on a flat table: if it rocks, or the screen edge sits proud of the frame on one side, the battery has swelled. That one is a fire risk, not a discount.
On an iPhone XR or newer running iOS 15.2 or later, scroll down the About screen to Parts and Service History. It lists the battery, display, and cameras that were ever replaced. Genuine Apple Part is fine. Unknown Part means a third-party component or one the phone can’t verify, and it often comes with a dimmer screen or a battery that reports no health number at all. Android phones have no equivalent, so a replaced screen shows only in the color: hold it next to another phone on a white page and look for a yellow or blue cast.
Register your own fingerprint or face during setup, then lock and unlock the phone a few times. A sensor that misses half the time is a damaged or swapped part, and on an iPhone a repair shop can’t bring Face ID back.
Flood the screen with color
“Check the screen” is useless advice without a way to do it. A single dead pixel vanishes against a photo and jumps out against a solid fill. Open the phone dead pixel test on the phone, go full screen, and cycle white, red, green, blue, and black. A dot that stays dark on every color is dead. One that glows its own color is stuck.
Then run the phone backlight bleed test on a black fill in a shaded spot. Glowing patches along the edges are backlight bleed on an LCD. Cloudy blotches at the dark end of a gradient are mura on an OLED. On an OLED, also open the phone burn-in test on a flat gray. A faint ghost of the status bar or nav buttons there is burn-in, a permanent fault a quick look never shows. If the listing promises a 120Hz panel, run the phone refresh rate test. On Android, battery saver mode and budget panels often cap it at 60. An iPhone reading of 60 proves nothing yet: Safari holds web pages near 60 fps until you turn off a flag. Why ProMotion drops to 60Hz shows which flag, plus the settings that throttle the panel.
Paint the whole screen
A cracked digitizer leaves dead spots that a few random taps will miss. Open the touchscreen test, tap Full screen, and paint the grid slowly. Squares that won’t clear on a second pass mark glass that stopped reading touch. Press three or four fingers down at once and confirm the screen tracks all of them. Pull off any screen protector first, since a thick or peeling one fakes dead spots. Then tap Hands-off check, set the phone down unplugged, and keep your hands off it for the 10-second countdown. A touch that shows up on its own is a ghost touch, and with no charger attached it points to the digitizer.
Test both cameras
Open the phone camera test and switch between the front and rear camera. Both should show a live, sharp image. If one goes black and the other works, you know which camera is bad. Watch for heavy haze or specks that don’t move when you wipe the glass, a sign of dust or moisture inside the module. Step into a dim corner too. A camera that freezes or goes black in low light has a hardware fault, not just a grainy sensor.
Then open the camera app itself. Tap to focus on something a foot away, then on something across the street. A lens that hunts and never locks has a stuck focus motor. Fire the flash once. Shoot a ten-second video with sound and play it back: that one clip checks the rear camera, the stabilization, and the microphones in a single pass. Muffled audio or cutouts in the playback point to a damaged mic.
Play a tone through the speakers
Open the phone audio test and play a tone in the left, then the right channel. On a phone with stereo speakers, each side should fire on its own. A dead side or a buzz is the tell. If the sound is muffled, the phone may have water trapped in the grille. The water eject tool clears it in a 20-second cycle, and a speaker that clears up was just wet, not broken. The earpiece is its own speaker, and the call at the end of this list is what tests it.
Test the sensors, the buzz, and GPS
The parts you can’t see are the ones a seller never demos. Open the gyroscope test and tilt the phone. The dot should track your tilt with no lag and sit still when the phone is flat. A reading that drifts on its own is a worn motion sensor, the kind that ruins tilt games and auto-rotate.
On an Android phone, run the vibration test and feel for the buzz. A dead motor means silent calls and missed alarms, and it usually traces to a past drop. iPhones can’t run a web vibration test, so check the haptics by sending yourself a message instead.
Step outside and open the GPS test. It times how fast the phone locks on and shows the accuracy in meters. Under open sky a healthy receiver tightens under 20 meters in seconds. If it stalls in the hundreds out there, the GPS is weak.
Read the battery health
Battery wear costs you every day. It’s the one number sellers always skip. On an iPhone, open Settings, then Battery, then Battery Health and Charging, and read Maximum Capacity. Under 80 percent and a replacement is coming, so price that in. iPhone 15 and newer also show a Cycle Count on the About screen. Apple rates those batteries for 1,000 cycles before they drop to 80 percent, so 300 cycles is a lightly used phone and 800 is one near the end. Android buries it deeper. On a Samsung with One UI 6.1 or later, look under Settings, Battery, then Battery information. On a Pixel it sits under Settings, Battery. Most other phones need a free app like AccuBattery to estimate the wear.
Plug in your own cable and watch the percentage for two minutes. It should climb. A phone that charges only when the plug sits at an angle has a worn port, a cheap fix on some models and a board repair on others. A phone that runs warm and drains fast while you work through these tests is its own warning.
Make a call and check the network
Put in your SIM, or ask the seller to, and confirm the phone latches onto your carrier and places a call with clear audio on both ends. On an Android phone this is the carrier lock test too: no signal with your SIM means a locked phone or the wrong bands. Check that the model number in Settings matches your region, since a phone built for another market can drop to slow data or no signal at all on your carrier.
Join a Wi-Fi network and pair your earbuds. If you pay with the phone, confirm NFC turns on in Settings or tap it against a card reader. Each of those is its own antenna or chip, and a phone that took a drop can lose one while everything else works.
What a failed check does to the price
Some results end the meeting. A blacklisted IMEI, an account or management lock the seller can’t clear in front of you, a tripped liquid indicator, a swollen battery, ghost touches, burn-in, a dead camera, or Face ID that won’t enroll: none of those has a fair discount, because the repair costs more than the phone is worth or can’t be done at all.
Other results are a number. Battery under 80 percent is the maker’s out-of-warranty battery price, so look that up before you go and take it off the asking price. A few dead pixels, a worn charging port, a scratched back, a missing box, or an Unknown Part display on an iPhone are all worth a cut, and the size depends on how much they bother you. Match the price to a graded refurbished listing for the same model and storage. If the private seller isn’t clearly cheaper than that, the warranty on the refurbished unit wins.
The ten-minute order
- IMEI and blacklist, from the screenshot, before you leave home.
- Locks: Apple ID or Google account signed out, Carrier Lock line, device management empty.
- Liquid indicator, frame, and the flat-table test.
- Screen: dead pixels, backlight bleed, burn-in, refresh rate.
- Touch: paint the grid, four fingers, then the 10-second hands-off check.
- Both cameras, then one video clip with sound.
- Speakers, and the water eject cycle if they sound muffled.
- Gyroscope, vibration, and GPS outside.
- Battery health, cycle count, two minutes on your own cable.
- Your SIM: a call, Wi-Fi, Bluetooth, NFC.
Weigh the seller and the price
A clean test still leaves the question of who you’re buying from. A seller who meets in public, lets you run every check, and keeps the original box and receipt is worth more than one who rushes you to pay. If the price sits far below every refurbished listing for the same model, ask why. A graded refurbished phone from a shop costs a little more and comes with a warranty the parking lot doesn’t.