When I'm the buyer, my policy with feedback has always been to never give feedback before the seller. Feedback is meant to be about what each party is responsible for - buyer is responsible for payment, while the seller is responsible for shipping the item. As such, logically the buyer always earns feedback first (payment comes before shipping/receiving the item). Any seller who refuses to give feedback first, is not honouring the feedback system (each party must give honest feedback, without conditions). But we have sellers who get their money, but will only give feedback after the buyer gives feedback first.

Before the current system was brought in, I only had about 5% of sellers leave me feedback (some would harass me for it, and then refuse to 'take the chance' of giving it to me first, despite me earning it first). Now the ratio is about half, but I don't buy as much on ebay anymore, so my rating would have been 10 times what it is now if this new system had always been in place.

And for the record, as a seller, I always left feedback to all of my buyers.