There is a method to have bad feedback removed legally, I have done it but it takes a while.
You are allowed to send 5 feedback revision requests for every 1000 FEEDBACK received (Not transactions) but you have to make sure the buyer is actually willing to change the feedback from Negative to Positive. Negative to Neutral is a waste of time unless you are doing this for a change in your percentage and not your seller rating, as eBay considers a neutral rating the same as a negative rating. If you aren't sure and the buyer never responds to the request, it's used up.