I am logging in with some kind of local service that requires passport identity proof as well as that they prohibit one person from using other people's account (e.g. your friend). I don't know how they could find out if someone is using another one's account but I guess that when someone logs onto more then one account on the same device they will be able to detect by their system. OK. To put it simply, before paying for a phone, what can I do to test if the mobile phone is perfectly new and was not used or tested by other customers? Because I cannot control what they might have installed or even logged in. Or if it's just NO way to make sure the phone was not tried or played by any other people because they can always factory reset everything to make it look like a new phone?