There are a huge number of fake drive out there on eBay right now, they are generally smaller, faulty drives that have been reformatted to appear to have a larger capacity then they should.
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It's a simple enough scam, sell them for a reasonable price and because they appear to work and will certainly store a few GB of data most customers will be really happy with the product at that price. It won't be until much later that they are losing data and by then the seller will have moved to another account. By the time negative feedback appears on an auction site the seller will have pocketed 1000's.
One of the big clues is the manufacturer's don't actually supply drives with 64 or 128GB capacity.
I've just been involved in taking down a UK seller who was pushing 128GB Corsair Mini Voyagers where the largest legitimate capacity is 32GB. We think that by the time eBay closed the account they had made just over £1000 and are likely to turn up again with a new ID :(
It's the old story about a duck - if it waddles and quacks don't buy it!