In principle, I agree with Roger and Jeff. The buyer's responsibility after winning the auction is to pay quickly. The seller may, and should, leave feedback as soon as payment is received, or at least when the item is shipped.
In reality, that doesn't happen as often as it should. Sellers can no longer leave negative feedback for buyers. If the seller leaves positive feedback immediately, he leaves himself open to dishonest buyers holding him at ransom to get his positive feedback. And some buyer will make unreasonable demands and the seller has little or no choice but to accept the demands of get negative feedback.
As a buyer, I never leave feedback until I have received the item, examined it and tested it if necessary. If I encounter a problem, I contact the seller and try to work out a solution that's acceptable to both parties. Only as a last resort will I leave negative feedback.
As a seller, I leave feedback the same day I ship the item, which is usually the day after payment has been received, although I often ship the item the same day I get payment. That has been my policy ever since I started selling on e-Bay. Yes, I run the risk of being slammed by an unhappy seller. If there's a problem, I will take care of it even if it means a full refund without the need of returning the merchandise. Even so, the buyer may still leave negative feedback. Such is life on e-Bay.
Darrell, quiet...for now