Things can go wrong after payment. Lying about receiving a card, claiming it's damaged when it wasn't, being too unreasonable like badgering a seller for updates, etc. The actual payment is not the only part of the transaction to me as a buyer. Feedback by both sides should be done when the transaction is totally complete which happens when the buyer has the card in hand.
Supercollecting Josh Johnson (University of San Diego, Tampa Bay Buccaneers, Cincinnati Bengals, San Francisco 49ers)
Collecting Philip Rivers, Padres, Packers, Lakers, University of San Diego alumni
My Bucket, always selling and trading: http://s1204.photobucket.com/user/kramerattack/library/