Vendor ratings are pretty common and functional. I mean, hell, look at ebay if you want to see a prime example of work in action. As mentioned earlier, why operate to protect the exception while enabling those dirty scoundrel evil doers?

+1

The volume of ratings on Ebay gives a statistical advantage. A private seller that only has 2 ratings could end up getting a bad overall average based on one misunderstanding or deal going sideways.
Unfortunately, just as in law, the design is to protect the innocent even if it provides an unfair advantage to the "dirty scoundrel evil doers".

Not perfect, but it's the best we have.

Paying by paypal if you must pay online gives a big advantage as if you make one complaint they will pull the funds back from the person it was sent to immediately and hold until it is resolved.

+1