GADGET
You need to check the structure of the phone, i.e. how its body is, dents, scratches or other things.
Battery life is essential for a seamless user experience. Ask about the condition of the battery and get information about its performance and rate of wear and tear over time.
Check the market value of the phone model, compare the prices offered by other sellers to make sure you are getting a good deal.
Check the phone's camera quality and see how it performs. Check for lag, and other issues.
You need to make sure that the phone you are buying is compatible with your network provider.