Here's the $64,000 question.

Do you really believe that if the purchaser left feedback first and it was negative, regardless of the reason, that the buyer would not retaliate and do the same.
I'm sure there are cases, but I would say the percentage is VERY low.

I'm wondering why everyone seems to be using the word "HAPPY"
Feedback isn't left for the purpose of stroking someones emotions. It is left to demonstrate that the buyer OR seller has upheld his part of the bargin.
The transaction is divided into 2 parts seller and purchaser each has obligations and the feedback demonstrates fulfillment of each PART.

I'm curious how you would feel if the purchaser asked you to mail the item first and upon receipt
and their satisfaction they would mail payment.
Wouldn't that also be fair?
I don't want to go off on a tangent but why is the burden of trust always put on the purchaser.
Even if I have 300 positive feedbacks and the seller may have 5, Why am I expected to make payment first?