The biggest problem I see with the FB system now is this retalitory type use. The seller should be leaving feedback for the buyer concerning the payment, maybe communication upon the auction ending. What the sellers are now doing is not leaving feedback until the buyer does. I have started refusing to leave FB until the seller has left FB for my payment. The buyer's FB is to be use for the quality of the item and the shipping of that item. Did all of that meet the seller's auction verbage. I have communicated to my problem with this tactic and actually had a neg removed for it.
Under ebay rules one of the reason for removal of feedback is if the person participated in an eBay transaction with the intent of leaving feedback as part of a campaign to harass one or more members. Well when the seller does not leave feedback after being paid, he has now shown his intent to harass if the buyer leaves neg.
I will say most people shade their neg FB and create an emotional monster. I spend a long time when writing neg FB and do in in my own handwriting first to review it over time before entering it into the system. Sometimes it is good to get the monster going because he winds up using foul language in his response which is another reason to have FB removed.