Are the cards factory rejects ?? --- many manufacturers will offload their rejected cards to refurbishers who will repair them for resell but there are sites that will resell those units as wholesale products without actually repairing them so I'd be cautious (it's kind of like buying a product from a street vendor in NYC that buys factory rejects to sell to tourists cheap only to have the tourist get back to the hotel and find the insides of the product are missing and they just bought an empty case.) Remember the old saying "If it seems too good ..."
For that pricing I wouldn't be surprised if it was a lot of factory rejects or cards that were returned for warranty repair that they purchased and are reselling without ever opening -- sure some of them might be functional but they failed testing in the factory and did not meet specs to be sold as is so were offloaded cheaply to cover the cost of the components for either recycling or refurbishing by a third party (most manufacturers do that with their rejects to recoup at least some of the cost)