When trading in a phone, the company you are trading it in to will typically check the condition of the phone, the functionality of the phone, and any included accessories, such as the charger and headphones. They may also check to make sure the phone is not blacklisted or stolen. To ensure a smooth trading process, I would recommend wiping all data from your phone and making sure all of its components are in working order. It is also a good idea to bring the original box and any included accessories to the trade-in location.