I'm all for it, but not sure how it would work. The seller would post a price and a link to a paypal? Whoever goes through the purchase first wins?
I'm not too familiar with how Paypal sales can be adjusted, but are they able to only take one payment and halt any subsequent payments (on a non-merchant account)? That way you don't have three people sending payments and the seller having to refund two of them.
If we can make it easy for everyone to use and simple to understand, I think it is a good idea!