CEX have some VERY good prices on cards (I've had £200+ cards for less than £50 there) however there is the risk of them being fakes, although I've never had one myself I can see how it would be easy for someone to sell them a fake card. I would just look for a card that they dont have many in stock of that you know is fairly high end and should be ok - however the returns are good - take to any store for an instant refund