I'm at about 25% NPB, so I just have 'that' issue as part of my process. I have a numpty currently who I've not had contact from - have tried several times....
Long story short, I tried the Yahoo suggestion of 'Neutral Rating' - getting them to 'see me'.
The numpty returned a neutral to me!! Needless to say, more likely than not, I'm going to get my first negative outa this fool!!
I just wait a week, contact for a second time, then relist and report...
I'm very glad that we don't have to chase fees - then...I'd 'go'. I'm very hesitant to change the rating - more than 60% of my successful sales have been to users with 0 feedback...I hate to shut the door on business, and I was a newbie once too...

----- I may go that route if it becomes a bigger nightmare!!