Bias in reputation systems

A while ago, I ordered a memory extension at Amazon — or, rather, through Amazon. The first merchant took a while to not deliver; I called them, they tried to feed me some cheap excuses (which were rather obviously wrong). I cancelled my order, but that cancellation was only confirmed by the merchant once I tried to invoke Amazon’s guarantee.Overall, a pretty bad experience — this particular merchant didn’t do what they were supposed to do, they communicated badly, and they didn’t react in a timely way. Yet, I can’t give a rating in Amazon’s reputation system: After all, the order was cancelled… This suggests that some of the really bad merchants might have higher reputations there than they deserve, simply for the reason that the customers who were disappointed most heavily don’t get to rate them.(The memory extension has meanwhile arrived from a different merchant who got 5 out of 5 points for professionalism.)