I personally don't like the positive comments, either...if I'm going to try and negotiate with the seller a bit, it hurts me when he sees all the great comments and thinks his junk is worth more than it is.
Positive comments don't just hurt your negotiating position. I've had three people back out on sales where they posted an item for sale and I pm'ed I'd take it for their asking price then after seeing all the "deal of the day", "smoking deal" etc comments, they pull the sale. A couple were reposted later with a higher price. One of them said they with all the positive comments they had, he was getting offers for X amount more and they were going to see who offered the most. In that case the positive comments created an auction.