For the last couple of years eBay has aggressively enforced their guarantee for buyers. If the seller does not offer a refund then eBay will for up to 30 days after the sale and paypal has a similar guarantee that is good up to 180 days.
http://pages.ebay.com/help/policies/...guarantee.html
https://www.paypal.com/webapps/mpp/u...ale.x=en_US#13
As long as both companies offer this type of indemnification I am not sure how many sales of counterfeit goods would actually create an opportunity for a lawsuit.