Something similar has just happened to me - I received a negative rating out of the blue; going back through my records I found that I had actually interacted with the user 3 months ago - they had contacted me for a module I had listed, asking for photos - after I emailed the photos, they said they were no longer interested, apologizing for wasting my time. I'm confused they should rate me negatively three months later, and I believe it's not in line with how the system is intended to work (it says you should only rate a buyer or seller). I understand this is the simplest possible system and better than nothing (in almost all cases), but it would be great if there was a way to make sure it is not abused