Other than that, I'd ask how it would be handled if some petty/malicious person tried to deep six someone?
I'm worried about such possibility too.
I guess that since both parties would be able to leave feedback for each other, it should work as a deterrent for leaving comments in bad faith.
Of course, that raises the issue of someone asking to delete the other person's comments without deleting theirs.
I guess the main idea is not about negative comments, but about the presence of positive comments. So that people could "build up" their history.
Kind of like "good credit "vs. "no credit" instead of "good credit" vs. "bad credit".