I think it's a crud system. I checked mine, it shows 6 of my sales - all of these will be for some books I sold. They are all in the 'middle 50%'. But I know that my descriptions were absolutely spot on (I basically copied the cover descriptions, and included contents lists), my comms were excellent (winning bidder, despatch notes, etc), postage costs were exactly what Royal Mail charged, no extra at all, etc. If I had been one of my buyers, I would have absolutely no reason to put anything less than 5 stars - but obviously they didn't.