There are only 2 ways I can see someone having 98 flash drives to sell at 40% below what other eBay sellers are selling for:
[1] They are stolen. Unlikely here, since it would be hard to steal 98 of the same type of flash drive, or
[2] They are fake. This is much, much worse. eBay doesn’t care about people selling fake flash drives. These are Chinese knockoffs that are designed to corrupt your data (yes, it is true). What happens is they are really 8GB (or 4GB, 16GB, something less than 256GB), but are hacked to show that they have a much higher capacity. If you go to save 16GB of data, either just the first 8GB or the last 8GB gets saved, the rest gets silently deleted (with no error message). So you data is gone, and you may not know for years (e.g. if it is for backups). Worse, a file listing will show everything is good (since Windows doesn’t check to see if the files actually exist).
For #2, many people never find out, and those that do that complain will often get a reply from the seller along the lines of “Oh, it must be a bad drive, I’ll happily send you a new one” – and no negative feedback gets left. And when someone complains to eBay about the fraud, eBay looks and sees perhaps 99% positive feedback, and assumes all is well (and with eBay getting $245 from those 98 $25 items, they have incentive to let the fraud continue).
So with thumb drives, it is always buyer beware. If you have one, verify it (either use a tool to do so, or save the full capacity and make sure all files test OK). Never give a thumb drive as a gift unless you bought it from a very reputable source and it is not generic (generic thumb drives have their uses, but also much more likely to be fake).