Pete,
You as well as others that contributed to this thread have made some very valid points. It's appreciated.

I think however the scenario you post above is a real reach.
Can it happen? certainly. Does it happen? I'm sure. We don't however base our feedback comments to take into consideration these extreme cases.
I suppose its like saying the only reason I go to a ball game is to see a triple play. Those also happen but quite rarely.

I could pose what I would call a reverse scenario. I make a purchase, I make payment and payment is received. I post my positive feedback FIRST.
The seller discovers that he undervalued the item and starts sending me nasty e-mails stating I knew the real value, I ripped him off etc. I start getting calls at 2 A.M
What then ?..... I suppose the only thing to do is to give them your home phone #

I still maintain that these ebay transactions are divided into 2 parts and as each part is completed feedback should be left.
If the seller is SO anal that he insists on leaving feedback last, let him demonstrate his trust based on MY FEEDBACK and ship me the item first.