As for reproductions or fantasy pieces, ebay doesn't know for sure if what's listed is genuine so they probably won't pull the listing. I don't think ebay really cares to look into it.
but....
If the buyer receives the item and makes a claim the item isn't as listed, they can make a claim and THEY WILL WIN - PERIOD as ebay won't look into that either. Of course you can receive a genuine piece and send back a reproduction as ebay also won't look into that.
As for who is more important, the buyer of seller, the answer is neither. You can't buy if no one sells and you can't sell if no one buys. But for ebay, it's the seller that pays the bills. No seller is important enough though for them to spend some research time to make an educated decision.