4 years experience in the mobile industry taking trade ins for several companies and I knew not to touch this deal with a 10 foot pole. I would inspect phones in store, send them off, and still get denied occasionally. The slightest hint of water damage, a scratched up screen and body, user data still on the phone or the phone locked to an email account via Google or Apple would disqualify instantly. On rare occasion they would claim damage to the device that wasn't there, made me wonder if things got damaged in shipping.
Point is unless someone can inspect my phone and guarantee me my money face to face, I'm not sending my phone off for a trade in.