I'm old school on this one even though some sellers are going the positive feedback first route. If I'm the buyer and I've sent the money in a timely way and the buyer receives it, I've completed my primary obligation in the deal and should be eligible for positive feedback right at that point. If I'm the seller, on the other hand, I still need to deliver what I've sold as described in a timely way before my primary obligation is met and my feedback comes when I deliver on my end of the deal. If the seller witholds feedback until he has positive feedback, then it becomes one sided in favor of the seller and defeats the balance in the process. I just don't bother with feedback either way if I'm the buyer dealing with a seller who insists the buyer goes first.