I can't believe no one's really mentioned this expansion of eBay's fraud protection.
"The new program, called PayPal Buyer Protection, gives buyers up to $500 of free coverage if the item is not delivered or turns out to be "substantially not as described" if bought from certain eBay sellers. There is no processing fee.
In order to qualify, sellers must have positive comments from partners in at least 50 transactions, and must have positive feedback from at least 98% of all transactions".
This is probably the ultimate validation of reputation mechanisms on the net - or at least, by far the most significant one so far.