I knew that eBay was going to be a gigantic success way back in the 1990s when a friend, confronted with the problem of disposing of her deceased and very tall mother's collection of size 13 shoes, put them up for bid on the online marketplace. They were quickly gobbled up by a grateful crossdresser from Kansas City.
These days the shoe is on the other foot, so to speak, and eBay is under attack for selling knockoffs. Details from the New York Times here.
EBay's defense that it has no obligation to investigate counterfeit claims is unconvincing. Tiffany & Co. sure isn't buying, and has sued eBay for selling Tiffany fakes.
Meanwhile, I know from my own expertise in one area -- late 1960s and early 1970s psychedelic rock posters from San Francisco music venues -- that the buyer had indeed better beware, especially because the market in posters, always awash with fakes, is red hot right now and prices have tripled and quadrupled to stratospheric levels.
I cruise eBay looking for good buys from time to time and regularly find posters that seem too good to be true. Which means they almost certainly are.