What if the buyer claims the item never arrived? Claims it's broken? Starts demanding refunds?I disagree, I was actually on about this today.
I always feel the seller should leave feedback first, after all, when he's paid you there is nothing else for him to do. He's done his part perfectly by giving you payment. If I sell something I ALWAYS give positive feedback if someone pays me, even before I send the object out.
As a buyer, I don't think I've ever got feedback until I've given some. The large automated sellers always say 'if you give us positive feedback, we'll automatically give you some'.
As a seller, I've always waited for either feedback or a confirmation the item arrived and was OK before giving any.

