What deserves a bad review on Bunz to you?

To me, this is subjective but standing someone up or lying about the item should definitely get a bad review I never meet without a "review request" which I think shows that to some level this person is serious. Nevertheless, I've heard people say that they're afraid of giving bad reviews because they don't want to get a "revenge" bad review themselves. I wish that Bunz had a way to comment on your reviews to give your version in these cases. What do you think?