One aspect of this problem might be that there's no incentive to have a wider dynamic range in your ratings. A naive recommendation system which just suggests h

One aspect of this problem might be that there's no incentive to have a wider dynamic range in your ratings. A naive recommendation system which just suggests highly rated books similar in some metric to ones I rated highly could be improved enormously if it took into account books I didn't like. In return for accurate ratings, I would get good recommendations.