Might also help if the burn amount could be denoted as positive or negative. If zero is the worst, it might just mean "didn't care." If someone spends a significant sum on a negative rating, you know he was pissed.
There have been some behavioral economics experiments showing that people are quite willing to make sacrifices to punish offenders.
The burn amount shouldn't be proportional to the rating.
I realize now the system described above is faulty, as the vendor must not be able to hide transactions with a low rating. Also, of course the review value shouldn't be specified by the buyer before he has received the goods. But I'm pretty confident this can be worked around with the right protocol.
There have been some behavioral economics experiments showing that people are quite willing to make sacrifices to punish offenders.