Since no one can SEE function, and since it's clear that more people are worried about appearance than function (it's true), the ratings given are simply an estimate of the remaining moly dry-film finish remaining.  It's assumed (sometimes incorrectly) that any other problems are specifically spelled out (dents, scratches, broken floorplate tabs, etc.).

Many great looking mags don't function well, and many ratty-looking mags (including many of mine) work great.  But folks obsess about things like tiny scratches or wear marks, so there will always be people who buy based on appearance.

-Troy