If you are a buyer, I would not be to concerned about having a negative added. A seller is covered, because they still have the item till it's paid for.
I am much more concerned about feedback of those I buy from, than the ones that buy from me.
If you get a negative, keep a level head... (no name calling now... be professional...) respond and say what really happened. Those that look at feedback will be able to see for themselves.