I agree that selling knockoffs (and let's use plain language here, counterfeits) should be dealt with more firmly. Perhaps a version of the UID Strike policy would be helpful here?
It would also be useful if eBay would allow shipment of purported counterfeits to be sent to a North American address rather than demanding that the items be returned to Asia with Confirmation of Delivery. Perhaps a version of the Global Shipping Program? 
However, eBay does participate in the VERO program that does curtail much of the abuse that was happening a few years back. While most of the members of the program are manufacturers or designers of high end /high value items. The VERO program came out of the suit that eBay lost to Louis Vuitton.
Meanwhile, we can go with caveat emptor. If it sounds too good to be true, it probably is.