Keep in mind that the Gift thing is not just about avoiding scammers. Imagine some ways a transaction could go wrong: Package gets lost and seller didn't insure it; Buyer says the item he bought is not working properly and seller swears it was when he shipped it; Buyer/seller don't agree about condition/rating, etc.
A completely legit seller, who maybe has done 50 perfect transactions, might not have the cash to eat a $1000 lens that he didn't insure that got lost. Or that same seller may be "certain" that the $1000 lens must have been mucked up by the buyer, so why should be take it back. Or he might just feel that a buyer is being ridiculously picky. Whatever the case, if the buyer paid with Gift he has no recourse and no leverage.
I'm not suggesting that happens a lot, but I think it is pretty clear that despite the best intentions by all parties a transaction can go wrong. Why give up your rights as a buyer to save 3%?