I'm not sure how / what these folks who keep apparently getting scammed are buying, but I have ~200 books purchased in my history with 3/4 of them most likely used, and none have been fakes.

I constantly buy / add to my wishlist older hardcover books I'm interested in reading and will come back and check when the used price is low and buy either Like New / Very Good / Good and have been satisfied with the results. Nothing like getting a 800+ page hardcover book with barely any use delivered to your door for 6-10$.

If one is worried about quality don't by anything used that is less than Very Good IMO.