Feedback should be open, fair and based upon your true impression of a situation combined with evidence to justify your conclusions.
It is therefore annoying that, having bought something from an Amazon Marketplace seller and left negative feedback about their lack of communication when I complained, I received an email apologising (or rather explaining why it wasn't their fault) and offering me 10% of the purchase price back if I removed the negative feedback.
Interestingly, the seller didn't dispute the feedback, just asked that I delete it for a bribe partial refund.
Doesn't an approach such as that make the 99% 'good' feedback rating fairly irrelevant and pointless?