There's more than one way to look at this, Jim. The transaction isn't complete until both parties are happy. When the buyer pays in a timely manner, the seller is happy, but this is only the first half of the transaction. When the buyer receives the merchandise and is satisfied, then he is happy, and the transaction is complete. When the buyer gives his feedback, then the seller knows that a successful transaction has been completed. It has been my experience that only about 60% of buyers leave feedback, anyway.
As a seller who used to leave feedback as soon as I received payment, I found on more than one occasion that certain people turned out to be ballbusters, after I had already left them positive feedback. I'm not talking about legitimate claims like disagreements over condition grading. I usually offer a refund if the item is not in the condition I claimed it was in. I'm talking about people who were completely unreasonable. As a seller, I've never left negative feedback. If somebody stiffs me, I report them to Ebay. If somebody busts my balls, I block them from bidding with me in the future.
In regards to shipping delays, I've had customers give me grief over late deliveries that were not my fault. When you receive the item, check the shipping date. If it was shipped on the date that the seller claims to have shipped it, blame the post office.