It's not clear, however, how much money Amazon has made selling fakes, if any
I bet amazon make huge money on fakes, by sheer volume of trades in fakes. Looking at sd cards and usb flash drives, it's practically impossible to detect which is fake, and which is not. Until you realize this "genuine" SanDisk usb 128GB stick overwrites your irreplaceable files with another batch, because it's like, 16Gb at best :)
But the problem is twofold, it's not only Amazon and ebay that don't give a flying monkey about fakes (as long as profits exceed cost of returns and litigation), brands which don't care either. I tried to buy a replacement battery for a few year's old laptop. The most reliable vendor I chose, and I did try really hard, sold me a fake (not a no-brand replacement). I got my money back, but neither ebay nor original brand has a way to report fakes (and despite negative reviews, the seller keeps selling exactly the same battery, probably because people don't actually read negative reviews BEFORE buying :).
Apparently, there's no way to actually test if a flash stick is genuine, because fakers easily re-programm the controller, and sometimes show genuine sense of humour, selling 2Tb micro-sd cards. That said, I've recently spoken to a highly intelligent person, who happily admitted he'd bought such a card "knowing something's not right about such capacity". Yet, he was happy enough to waste about 8 quid, "to see what it's like" (I told him what it will be like, but still, he didn't mind!)
And then, having (thought) I educated my better half about the "value" of amazon reviews - she buys some shitty toy for our kids which turns out to be, well, shitty. Because it had so many good reviews... Sure, I sent it back, we got the (shitty) money back, but if they flog 100 boxes like that, and only a few people bother to return it, business is booming, brother!
So, essentially, it's a downward spiral, when all sides of a transaction know it's fake, or probably fake, or maybe-fake, vendor, platform and buyer, yet knowingly engage in this sale.