A few of these only have one seller. Money laundering? A different algorithmical problem? Something else?

Could be this: If two sellers have the book, and are setting the prices algorithmically, and then one of them sells it offline (like in a used bookshop) and removes it from sale, how does the other seller change their price to be more realistic?

Several are from the same vendor. I think there are some very sloppy resellers on Amazon.