Hello, Personally I wouldn't recommend anyone to buy a used phone since you don't know what the previous owners did with it and also since there is a high chance that the phone will be in a worse condition than that of a new one, but if you have to buy a used phone I would recommend you to mainly check these out: - Make sure it's not a stolen phone - Battery condition (How much of the battery life has been used and if the battery is in good shape) - Phone specs (before you buy a phone you have to know what it offers you) - Touchscreen and Button conditions - Camera (both front and back) condition - Microphone and Speakers (both the Handset and the loud speaker) - Ports (check different ports on the phone such as the charger port and the headphone jack) - Software condition (check the operating system and default apps) - Android version (Android versions 6.0 and older are now considered old and a lot of apps might not work on them) - Do a test of the sensors - After all this first try the phone for a couple of minutes before you buy it, open different Apps and check how it reacts. Check if the phone dialer app works correctly. - Last but not least, make sure the phone has been formatted and all google or iCloud and various accounts have been removed