I'm not 100% sure on Amazon GC but I know if they are payed for with a CC then that can be reversed and there is also the risk of it being already used or Amazon getting the money back if they have a lost/stolen card policy which I don't know if they do. If the card is bought with cash and you check Amazon's policies then it should be safe. Also, (s)he could be making legitimate offer and this may just all be in vain. Got to love the internet.

Edit: looked at the amazon site and the way I interpret their gift card terms and conditions, if the card is a physical card, bought with cash then they take no responsibility for lost or stolen cards. If it is bought online, then the purchaser can get a new card reissued by contacting Amazon.