I'm not trying to step on any toes here...and perhaps I haven't thought this through completely, but why not use a 3rd party feedback system that is already in place like heatware.com?
No worries! I expect my toes to be stepped on when coming up with new ideas. 
I wanted to create something that was bitcoin-centric. Heatware can't tell you whether a bitcoin address is indeed associated with the user account at heatware. I could just tell you that "oh hey, my username on heatware is blah blah", and if blah blah had a good rating, then they might believe me.
Unless, there's more to heatware than meets the eye... still, I like the idea of being able to verify that a seller/merchant is attached to a particular bitcoin address instantly.