My suggestion would be to eliminate the current system altoghether.  The fair way to rate users is how they complete transactions.  For instance, sellers would be rated by how quickly they ship, how many buyer complaints they have, how many Ebay and Paypal disputes they have had filed against them, and how many times they failed to complete a transaction due to inventory problems or any other reason.  Buyers could be rated based on things like how quickly they pay for an item, how many unpaid item strikes they have, and how many times they have filed complaints against sellers.

This system would take the current opinion based system and replace it with a system that used hard statistics based on the details of the transaction.  There would be an honest and fair system that ACCURATELY rated users on how well they complete transactions as both a buyer and a seller.

However, until sellers are willling to take action to fight the current system, Ebay will harm us buy playing favorites with the buyers.