Frontierman, your 3 NPB's in 500 transactions works out to six-tenths of one percent of the time. Not a very high rate of frequency, I'd say. Anyhow, when you say a buyer can always cancel a bid, you're overlooking the very specific reasons for which eBay will allow a bid to be cancelled:
"> You accidentally enter a wrong bid amount. For instance, you bid $99.50 instead of $9.95.
(If this occurs you will need to quickly re-enter the correct bid amount).
> The description of an item you have bid on has changed significantly.
> You cannot reach the seller. This means that you have tried calling the seller and his or her phone number doesn't work, or you have tried emailing a message to the seller and it comes back undeliverable."
In general I agree that deadbeats shouldn't expect much sympathy. But let's temper your decree with just a little bit of mercy: sometimes there's a valid reason for nonpayment within the time allotted by eBay, so cut the buyer some slack. As a seller I try to give a NPB at least 3 weeks and multiple e-mails before writing him off and leaving negative feedback, etc.