Bob as I said in a previous post on this issue, when I a sell on Ebay I wait for some indication from the buyer that the transcation is over. It could be an email telling me they received the item or they leave feedback.

Feedback should indicate your satisfaction or dissatisfaction with the other party on the entirety of the transaction not just whether you sent payment on time.

I can imagine all kinds of scenarions where a buyer pays promptly and properly but turns out to be a horrible buyer and deserving of negative feedback.

I do however agree with you that it is improper for a seller to require you to leave feedback first, this distorts the whole feedback system be discouraging negative feedback under threat of retaliation.