We'd best keep an eye on the situation so that we can see how this plays out in reality. If sellers are going to be at risk with false claims of "Fake! Fake!", I hope we can find a way to help all genuine sellers deal with this.
I'm a buyer rather than a seller, but I dread to think about the increasing vulnerability of sellers. Of course there's been a problem with some fake items being bought by buyers, but I don't think this is the way to handle it! Most of the stories of fake items I've read include the item being vastly, VASTLY cheaper than the genuine item - the buyers in some instances should have known that they were buying an imitation. It's a bit like a tourist in Egypt being told by a raggedly dressed urchin, "Mister, mister, I show you priceless antiques from King Tut! Very genuine, very good. You like. Very cheap. Pay only twenty american dollar. Genuine antique, I guarantee you, not like other urchins hawking fake items, only good stuff, I promise you." The tourist who hands over twenty US dollars for the item in question has fallen for one of the oldest cons of all - cheap genuine antique, attested to be genuine and antique by a BOY IN RAGGED CLOTHING.
The eBay seller who does something similar is not really a great deal more sophisticated, because it's the cheapness of the price which gives away the fact that this is NOT genuine - oh, and the fact that a look at the seller's completed listings include a whole ream of the Genuine Antique Crystal Ball which is supposedly one-of-a-kind, found hidden in the seller's aunt's attic or something.
A little bit of checking by the buyer, and the fakery is uncovered. Reluctance to check by the buyer can sometimes be a symptom of living in cloud-cuckoo land, not wanting to realise that the bargain is a fake and preferring to live in deluded hope of its being genuine. Has the buyer no responsibility at all to take reasonable precautions?
But... does eBay have any responsibility for what people sell on it? Yes - there have been precedent-affirming cases in which markets have been held accountable for what market stall owners have been selling (fakes, fakes and more fakes). So eBay has a responsibility - but is that responsibility met by enabling buyers to declare that the item purchased is a fake after the fact? Isn't the responsibility of eBay more pre-emptive than post-op? Isn't the post-op option enabling fraud on a large level?
How DOES the buyer establish that the item purchased is a fraud?
It's been a thorny question for a while. Sometimes eBay/PayPal would not accept anything except a signed statement on letterhead from the company making the original item - and of course that's impractical for many things. A stat dec has always had a significant weight in any such questions... but I worry that the way chosen now by eBay is an abdication of responsibility - moving so far from one position that the whole thing tips over, to genuine sellers' detriment.
As I said, let's see how it plays out. Perhaps in practical terms it won't be as easy to defraud as I fear...