From the other side of the equation: my grandpa runs the Amazon storefront for a charity for which he volunteers (said charity sells donated books in support of the local library system). He sells the big-ticket stuff on Amazon (usually at a fraction of the lowest price, which still brings in plenty of money given the acquisition cost is effectively zero), and anything not valuable enough to break even on shipping (or otherwise doesn't get sold on Amazon) gets sold in a physical storefront next to one of the libraries (big-ticket books being sold individually, and the other books being sold in bulk by the customer filling a plastic shopping bag full of books at a flat rate).

One of the weird things about Amazon is that it doesn't give you an easy way to provide photos for the item you yourself are selling (e.g. your used copy of a book), and if your item is similar enough to an existing item (e.g. same UPC or ISBN or whatever), Amazon will railroad you toward using the existing listing (but will still put you in the "new and used" list).

In other words: the same Amazon quirks that seem to benefit counterfeiters also seem to benefit my grandpa's charity, so I guess I should be grateful and appreciative when I get a knockoff at my doorstep.