Before you buy
Checking a used phone before you buy
A used phone hides its faults better than a laptop does, because the one part that costs most to replace is the one you are looking straight through. This is the order that finds the expensive problems first — and the four checks that matter most are not browser tests at all.
The run, in order
Ask for the IMEI and check it before anything else
Dial *#06# to show it, then check it on your carrier or a national blacklist service. A blocked or reported-stolen handset is worth nothing to you no matter how well it works, and this is the one finding that should end the meeting rather than the negotiation. Thirty seconds, and it costs nothing.
Check the phone is not locked to someone else
On iPhone, Settings, General, Transfer or Reset — if Activation Lock is on and the seller cannot sign out, the phone will be a brick after the first reset. On Android, check the Google account has been removed. Both are common on stolen and on casually resold phones, and neither can be undone by you.
Drag a finger over the whole screen and find the areas that do not answer
The screen is the most expensive part of the phone, the digitiser fails independently of the display, and a dead band is invisible until you try to type on it. Cover the edges and the corners, which is where impact damage lands.
Fill the screen with solid colours
Takes twenty seconds and finds what a wallpaper hides. On a phone the panel and the glass are one part, so a dead pixel means the same replacement as a crack.
Put five fingers on the screen and move them
A cheap replacement screen usually passes the coverage test and fails this one — it tracks a single finger but loses contacts when several move. That tells you the screen has already been replaced once, which is worth knowing before you pay for an original.
Check the battery health figure, not the charge level
iPhone: Settings, Battery, Battery Health and Charging — the maximum capacity figure. Android varies by maker and often needs a dialler code or an app, so ask the seller to show it. Under 80% is a battery you will be replacing, and that is a number to negotiate with rather than a reason to leave.
Tip the phone and watch the level follow
Sensors are cheap to ignore and irritating to live without: a broken accelerometer means the screen never rotates, and a confused magnetometer means maps point the wrong way for ever. They also fail from the same drops that crack screens, so a fault here suggests looking harder at everything else.
Open the camera and look at the picture
Check the front camera here, then open the phone camera app and check every lens on the back — a browser sees one camera, and a modern phone has three. Look for dust inside the lens and for a picture that will not focus, both of which are common after a drop.
Talk and play the recording back
A phone has several microphones and a call uses more than one. Twenty seconds here catches the one fault that makes a phone useless for its main purpose and that nobody thinks to test in a shop.
Play the left and right channels
Also listen through the earpiece by making a call if you can. A blown speaker is cheap to live with and useful to find, and it is one of the more common consequences of water.
Step outside and watch the radius fall
The one test on this list that cannot be done in a shop. A working receiver drops the radius under fifteen metres within a minute of open sky; one that stays at Wi-Fi accuracy outdoors has a failed antenna or a bad repair behind it, and both cost real money. It also fails from the same drops and water that damage everything else, so a fault here is a reason to look harder at the rest.
Look for the water damage indicator, and plug in a charger
The indicator is a small sticker that turns red or pink when wet — in the SIM tray on an iPhone, and in the tray or the port on most Android phones. Then charge for a minute with your own cable while moving it gently: a worn charging port is very common on a phone a few years old and gets worse quickly.
Do it in this order
The first two steps take under a minute and can end the meeting. Do them before you look at anything else: there is no point testing the cameras on a phone that will be blocked next week.
After that the order runs from the most expensive fault to the cheapest, so if something ends the deal you find out early rather than after twenty minutes of politeness.
What each finding is worth
| What you find | What it means for the price |
|---|---|
| IMEI blocked or reported | Walk away |
| Activation lock the seller cannot clear | Walk away |
| Dead zone on the touchscreen | Walk away, or the price of a screen off |
| Dead pixel | The price of a screen off — same part |
| Multi-touch losing contacts | Screen already replaced; pay accordingly |
| Battery health under 80% | The price of a battery off |
| Water indicator triggered | Walk away unless the price reflects real risk |
| Charging port loose | Small discount, but it will get worse |
| Dead sensor | Small discount; check for other drop damage |
| One speaker or mic dead | Small discount |
The pattern worth knowing
Phones fail from two events: drops and water. Both leave more than one trace, which is why the order above is worth following rather than cherry-picking.
A drop shows up as a screen fault and a sensor fault and a camera that will not focus. Water shows up as a triggered indicator and a dead speaker and a charging port that has to be wiggled. Finding two related faults is much worse news than finding one, because it tells you what happened to the phone rather than what is wrong with it — and phones that have been swimming keep failing for months afterwards.
Before you hand over money
Have the seller do a full reset in front of you and set the phone up far enough to confirm it is not asking for someone else’s account. A phone that resets cleanly and reaches the setup screen is a phone you can actually use, and it is the last thing that can still go wrong after everything above has passed.
Common questions
What should end the deal immediately?
Three things, and all three are checks rather than tests: an IMEI that is blocked or reported, an activation lock the seller cannot remove, and a screen fault. The first two make the phone worthless to you whatever its condition; the third costs a large fraction of what you are paying. Everything else on this page is a discount rather than a reason to walk away.
The seller says the screen was replaced. Is that bad?
Not automatically, but it changes what you should check and what you should pay. Replacement screens vary enormously: a good one is indistinguishable, a cheap one loses multi-touch contacts, shows worse colour, and sometimes disables features tied to the original panel — Face ID on an iPhone in particular. Run the multi-touch and colour tests specifically, and expect a lower price.
Can I check the battery on an Android?
Less easily than on an iPhone, and it varies by manufacturer. Samsung exposes it in Samsung Members, some phones respond to a dialler code, and otherwise it takes an app. If the seller will not show you a number, treat the battery as unknown and price it accordingly — a replacement is not expensive, but it is not free either.
How long does this take?
The browser tests are about five minutes. The IMEI, the lock, the battery figure, the water indicator and the charging port add another five, and those are the ones that matter most. If the seller will not give you ten minutes with the phone unlocked, that is an answer in itself.
Do I need to install anything?
No. Every test here runs in the browser on the phone you are inspecting, so you need nothing but the address of this page. Nothing is uploaded and nothing is left behind on their device — which is also why you can hand the phone back without clearing anything.