My understanding from Gamestop was that they won't buy them because the characters cannot be fully reset. I haven't tested it, as you asked, but given that this particular Gamestop is run by intelligent people, I would assume they cannot be fully reset.
Batman: Arkham City was the best game I've played this year. Then came Skyrim.
I don't understand what the issue would be. Its no different than buy/reselling a used video game or memory card. You don't know if it has a owner until you place it on a portal. At that point you either become the owner (if its new) or you can take ownership of it (used) .
Arent things like DS games still cartridge?? Can't they still have save files from the previous owner?? I dont see GameStop refusing to trade/purchase used DS games because of it. If customers are to ignorant to reset ownership of a figure they shouldnt be playing the game in the first place.