Well, I must say I've gotten some really GREAT stuff on Ebay, many sellers are very honest. And as a collector of many things, Ebay has been the only place I can find some things.
If you study how to buy on ebay, and have a little bit of knowledge how sellers work, you can usually spot a scam, or other dishonest sellers.
My favorite yarn seller ever is an ebay seller. I get such Fabulous yarn in spools at rock-bottom prices. Yarn like chenelle, 100 % wool, loopy yarn and eyelash up to 5 pound spools for as little as $5. FAST shipment and very honest seller. She combines shipping and handling for more than one purchase too.
So it helps to search out what you want, know your market, learn strategies, and be a little brave with your faith in humanity when you buy from a new seller.