So after receiving my shiny new jet black 128gb on Friday I decided to trade in my iPhone 6 64gb to game, seems to be the best price at the moment... the process ain't smooth, first waited 25 minutes, then a 10 minute argument with the very knowledgeable chap behind the counter. Apparently according to him all iPhones sold by apple are auto locked to the first network sim interested, he has bought all his iPhones from apple and that happened to him, told him he was incorrect a few times which seemed to make him a little mad, would only offer grade C price for a pristine condition phone, was expecting grade B at least given the phone has been cased since I got it and all original accessories are in the box.
I left the store at that point and will try another store, maybe it was the end of hard day but dearly me it was hard work
Maybe he fancied it for himself & was looking for a nice price! You did the right thing IMO, smile & walk