You can respond to feedback about you in your 
feedback forum so It'll be listed directly under 
the feedback they left you.  You can also 
petition e-Bay to get the negative removed (but 
let's face it, it's easier to swim to China).  

If the person has low feedback or lots of negs, 
I would just respond that it was retaliatory 
feedback and the reader should go look at the 
other person's feedback.

I'm sorry! >_< that sucks.