Getting negative feedback, especially if you feel it was undeserved (e.g. from an impatient member, someone suffering from overbid guilt, etc), can spoil what would otherwise be a perfect record. eBay has a procedure where members can apply to have negative feedback removed, but this is only allowed under certain circumstances, such as obscenity, mistaken identity, posting private information, etc.
So where does this leave you if you feel hard done by an unfair comment?
However angry or upset you may be, retaliating with anger won't help the situation. Contact the other party calmly, and try to understand why they left the comment. Explain your side of the situation, especially if it was caused by something beyond your control e.g. postal misdirection, customs delays, etc.
Some kind words and diplomacy can work wonders, and ask the other party if they will consider a mutual withdrawal of the feedback. Although the comments won't disappear, at least the negative now won't count against your score.
And don't forget, both parties can also add a follow-up to the negative comment explaining how it was resolved.