A used phone does not need to look new. The important question is whether the wear is honestly described and whether it points to a functional, safety or repair-cost problem. Check the phone as a connected system rather than treating each scratch in isolation.
In brief: stop for swelling, a lifted display, unusual heat, account locks, a bent frame or intermittent core functions. Price cosmetic wear separately from faults.
Physical warning signs
| Sign | Possible concern | Practical response |
|---|---|---|
| Display lifting from the frame | Battery swelling, poor repair or frame damage | Do not charge; reject or obtain professional assessment |
| Bent chassis or uneven gaps | Impact damage and pressure on internal parts | Check screen, cameras, buttons and sealing; usually walk away |
| Cracked camera cover | Image defects and moisture or dust entry | Test every lens and include repair cost |
| Damage around charging port | Intermittent charging or previous forced connection | Test cable movement, data and charging |
| Corrosion or residue | Possible liquid exposure | Do not rely on present function as proof of future reliability |
Liquid indicators and water-resistance claims are not complete diagnostic tools. Water resistance can reduce through wear or repair, and a phone that works today can still develop corrosion-related faults later.
Screen and touch problems
- dead or stuck pixels;
- lines, flicker or unusual tint;
- touch failing near an edge;
- ghost touches without contact;
- brightness changing abruptly;
- poor alignment, lifting or adhesive residue after replacement.
Test the whole display with a plain light and dark background, then type across the keyboard and drag an icon around the edges. A cheap replacement screen is not automatically unusable, but it should match the listing and perform reliably.
Battery and heat warning signs
A battery can be worn without being unsafe. The strongest concerns are physical swelling, shutdowns under light load, rapid percentage jumps, severe heat during ordinary use or charging that stops unpredictably.
Use the manufacturer's diagnostic information where available. Do not rely on a single third-party percentage as proof of battery condition across every Android model.
Cameras, audio and connectivity
Test each rear lens, the front camera, focus, stabilisation and flash. Record audio, play it through the speaker, make a call and test the microphone in more than one app where possible. Check Wi-Fi, Bluetooth, mobile service and GPS.
A fault that appears only intermittently is still relevant. Record it rather than repeatedly resetting the phone until the symptom disappears.
Account, management and software red flags
- Activation Lock or a request for the previous Apple Account;
- Android setup requesting the previous Google Account after reset;
- company or school management enrolment;
- IMEI mismatch between settings, dialler, box and receipt;
- software that cannot update despite the model still being supported;
- persistent repair or parts warnings not disclosed by the seller.
When a lower price is not enough
Calculate the cost of the likely repair, the remaining support period and the risk of another hidden fault. A £50 saving is poor value if it introduces a £150 screen repair or leaves you without a workable return route.
For a broader inspection, use the Used iPhone Buying Checklist, Used Android Phone Buying Checklist and Cosmetic Damage vs Functional Damage.
Sources and date checked
- Apple Support: If you want to buy a pre-owned iPhone
- Apple Support: iPhone Parts and Service History
- Samsung UK: Samsung Members Diagnostics
Facts checked: 25 July 2026.
