You can respond to negative feedback - I did, in no uncertain terms and the seller backed down at once. Don't agree to removing the negative feedback until you have what you want, as you can't put up any further feedback after a mutual removal has gone through.

I was eventually refunded some of the cost - but you have to complain within the time limit - and a lot of sellers will string you along until after the alotted time has passed and then just drop the matter, as they know the rules.