I'll buy even with a few negs, depends on what they are. I saw a great one while shopping for my bb. Someone left a negative because the display phone they bought didn't work. The auction had huge letters describing the display phone, how it was just a display phone and didn't work, blah blah. Yes still left a negative.
I also look at the responses. Even if you are right, if you respond to a negative with "guy is big jerk, little man syndrome" or other completely unrelated name calling...I avoid you like the plague!