Buying a used phone, laptop or tablet: a pre-purchase checklist

1. Activation lock and accounts

This is the most important check. A phone or laptop still tied to the previous owner's account can be locked remotely and may be unusable. Ask the seller to sign out of their account and factory-reset the device in front of you. On an iPhone, "Find My" must be turned off; on Android, the Google account must be removed before reset.

2. IMEI and carrier status

Dial *#06# to show the IMEI and make sure it matches the box or the settings screen. Many carriers and national registries let you check whether an IMEI has been reported lost or stolen. Also confirm whether the phone is unlocked or tied to a carrier.

3. Battery health

iPhones show battery health under Settings → Battery. Many Android phones and laptops show it in settings or a diagnostics menu. A battery that is noticeably degraded is not a deal-breaker, but it should be reflected in the price.

4. Screen and body

Look at the screen on a plain white and a plain black background to spot dead pixels, burn-in or discoloured patches. Check corners for dents, and look at the edges for gaps that suggest a swollen battery — a swollen battery is a safety issue, walk away.

5. Functions you'll actually use

Run through the basics:

• Charge it with your own cable for a minute.
• Make a call or play audio through the speaker and the earpiece.
• Test front and rear cameras and the flash.
• Test buttons, fingerprint or face unlock, Wi-Fi and Bluetooth.
• On a laptop: every key, the trackpad, every port, the webcam.

6. Paperwork and price

A receipt or original box is a good sign but not proof. Compare the price with recently sold examples of the same model and storage. If the price is far below everyone else's, assume there is a reason until you have found it.