I'd bet 90% of the ebay cards are counterfeit. I've gotten burned on every one I've ever bought on ebay (well not burned--paypal has always come through with a refund). The ones I got were actually smaller cards hacked to report larger sizes. When you get above the actual size, it starts overwriting files already on the card (at least this was my experience with a card reporting itself as 64G, but only held 32G before giving errors on the files already there).