I know this would be a pain to implement, but what about if a buyer had to "buy" a buyers account and then that buyer has a credit of said money. So, if a buyers account cost 5btc he would get it back in product purchases. I don't know if this would stop scammer buyers/bogus feedback but its a thought. Or to make a buyers account you need to deposit 10 btc's into your account. That would help stop all the new buyer accounts and that buyer would need to spend those btc's. so most likely it would be on multiple transactions. Or have a 20btc deposit minimum.