I buy a lot of really bad books on Amazon. They’re minor books, on fringe topics, and they’re usually well out of date. They’re also usually incredibly cheap, like two or three dollars, or some such. And while they’re generally pretty uninteresting, they can often offer a citation to support a minor point in a literature review. (Citations don’t always need to be to authoritative sources. Citing an obscure work can also help make an argument, in a different way.)
So while I use these books for my research, I don’t really want to own a copy. But I buy them anyway. This is because Amazon is often the most effective way to get a hold of them. These books are usually such trash that most libraries that might have once held a copy have long since discarded them. Spending $3 on Amazon is less of a headache than trying to coordinate an ILL from a distant library. Leaving aside the obvious privilege of making such frivolous purchases, and the ethics of buying from a company like Amazon, buying trash books is really a pretty good solution.