The way you avoid this problem is to avoid creating the incentive to subvert the loop.

I am fairly confident that every metric, target, index, goal, KPI or score that has ever been connected to money, power or fame has been subverted. As far as that goes, yes, I see the world as black-and-white.

Glassdoor scores are tied to ability to hire. It's easier to game the scores than to not suck, especially since "horrible place to work" is going to correlate strongly with "dubious ethics".