Well, “responding with very neutral language” could portray the Seller as accepting responsibility for the bad review. If a Buyer left unfair remarks, there’s nothing wrong in telling your side, exactly as it is - neutral language or not. If I were a Buyer and spotted such Seller’s counter response, I’d rather check the frequency of the good reviews he had as well as the quality of his portfolio items to decide wether to patronize or not. If I have such opportunity to respond to Buyer’s negative review, I won’t be diplomatic.