They are bought with hacked/stolen credit card info. That is why they regularly go bad. Obviously "sofia" has no problem sending a new card because it doesn't cost them anything. Beware involving yourself in this credit card fraud scheme. They are doing just what is talked about in this article:
http://wishtv.com/2014/11/06/thieves-use-gift-cards-to-cover-up-credit-card-fraud/
They sell for btc cause there is no way for it to be charged back, and they can operate from anywhere in the world. Also, that is the only explination for selling for 70% off here, rather than the going rate of about 20% off on ebay. Like they say if something sounds too good to be true, it probably is!
your ebay example is way off. it is the same cgards sold on ebay as are sold here just for more money. i had $300 worth of cards go bad from ebay that i paid almost 85% for. you think just because they are more expensive and sold on ebay they are ok? that being said i have bought a number of cards for various sellers here and all have remained good. i'd rather take a chance at 30% than at 85%.
Never did I say eBay cards are all legit. I just said they go for more there, which they do go for 70-90% of face value. But obviously this "Sofia" sticks to btc so they can't be traced or charged back.