What a phone diagnostic test checks before you sell
14 October 2026 · 5 min read
When a buyer inspects a used phone, a lot of what they check can't be seen by looking at it. A diagnostic test is software that checks the hardware directly. Here's what a professional test covers, what it can't see, and why running one before you sell changes the deal.
What a diagnostic checks
Professional platforms such as Phonecheck, which is widely used by refurbishers and marketplaces, run a structured set of tests. Typical coverage includes:
- Battery: health (how much of its original capacity it still holds) and charging.
- Display and touch: dead pixels, touch response across the whole screen, brightness.
- Cameras: front and rear cameras, focus and flash.
- Sound: speakers and microphones.
- Sensors: proximity, accelerometer, gyroscope, compass and similar.
- Buttons and ports: power, volume and other physical controls.
- Connectivity: mobile signal, Wi-Fi and Bluetooth.
- Biometrics: Face ID or fingerprint, where the phone has them.
- Parts history: on many phones, whether key parts have been replaced with non-original ones.
Identity checks: the part people don't think about
A diagnostic also reads the phone's identity: its IMEI (the unique number for each phone's mobile radio) or serial number, together with the model and storage. That identity can then be checked against:
- Blacklists of phones reported lost or stolen.
- Activation lock status, such as Find My or Google account protection.
This protects everyone. A buyer won't pay for a phone it can't resell, and a seller learns about a problem before posting the phone rather than after.
What a diagnostic can't see
Software can only test what the hardware reports. It won't reliably spot:
- a cracked or chipped screen, if touch still works;
- cracked back glass; or
- liquid damage that hasn't yet caused a fault.
These are the things to check with your own eyes, and to describe honestly to any buyer.
Why testing before you sell matters
On most trade-in sites the inspection happens after you've posted the phone, and that's where offers get revised (we explain the pattern in why trade-in offers drop). When the test runs first, on the phone where it is, the price can be set from facts instead of a description. The thing that would otherwise be argued about on arrival has already been settled.
The same test is what lets a buyer stand behind a price: if they know the battery health, the state of every component and that the IMEI is clean, there's no reason to change the offer when the phone turns up.
How it works with ClearFrank
ClearFrank uses the Phonecheck platform. You install the free Phonecheck app, scan a code to connect it, and follow the on-screen tests. It takes about five minutes, and the app reads device health only, not your personal content. The result is what your price is based on.