QA involves more than just testing - verifying vendors, checking their bona fides, and having relationships/terms that allow for more than just no fault returns for fraudulent suppliers.

Amazon basically has the same broken dynamic as other centralizers like Youtube. They want to promiscuously accept suppliers as if they themselves are just a neutral conduit, while also performing discovery/recommendation across those listings. These are two very different things, and the conflation of them makes it so the barrier to getting in search results / recommended is an afterthought. If the fraudulent books were only reached because OP had come in through a link recommended elsewhere, there wouldn't be too much to take Amazon to task for. The problem is that they're discoverable through their own branded search, hence the blame of quality (or in this case, abject fraud) landing at Amazon's feet.

> How do you do QA on one-off items or reliably fact check books?

There’s a reason that traditional publishers don’t just take manuscripts and print them without active review and engagement, and there’s a reason traditional book retailers have buyers. Amazon (both as a publisher and retailer) and other online marketplaces have treated it as if the only reason for these things was resource limitations of the traditional marketplace (whether imposed by printing, etc., costs for publishers or inventory and shelf space concerns for traditional retailers) but it also goes to customer trust.

Does it scale? No, but if you don’t do something like it, then you may have an infinite number of titles, but it will become impossible for customers to find anything that has quality among the trash.

Presumably someone would read the books. Normally, this is done by the publisher, which decides which books it wants to publish. The bookstore decides which publishers it wants to work with.