Is there a "quality filter" setting you can toggle on and off? Who decides what goes on which side of the filter? At Amazon's scale, it would have to be automated.

Much like search SEO and every other algorithm, people would start to figure out how to game it, and eventually Amazon would give up trying to police it because it would cost them more money than it's worth, and you're back to where you started except now you have an additional - and inaccurate - "quality" attribute on every product.