I upgraded my iPhone to a 7 and had an unlocked 64gB iPhone 6s to sell, in perfect condition. I went on a price comparison site and music magpie quoted £270 so I "sold" it and a courier picked it up. Within a day I received an email saying I had a revised offer of £150 due to "substantial damage" on the phone. It was in mint condition when I sold it! I declined the offer and it was returned to me. There were stickers all over the screen indicating the "damage" - a scratch had appeared!! DO NOT USE THEM!! As an aside I went to a local Game store and sold it for £200!!!