I guess, from the above posts, that anyone can add positive feedback under any circumstances. But just know that only with a completed auction (someone is declared the winner and reserve is met) can feedback be left, by the seller or bidder, that will affect someone's FEEDBACK RATING (the number that appears in parentheses after one's eBay ID or e-mail address). Also, you can leave feedback for each completed auction, but it will increase the FEEDBACK RATING just once; that is, after the first time, more feedback by the same person for a particular person won't increase the RATING. (In case I garbled this, let me put it this way: A and B are winning buyers and sellers in many of each other's auctions. They may leave feedback many times for each other, but they can only increase the other's FEEDBACK RATING once.)

Robert