The way things work at my university, at least the science faculty, is that word of good or bad teachers just travels trough the grapevine. And it is usually quite accurate.

Then we have (a active, and paid) representation in the faculties decision making body, which leads to, in my experience, the faculty actually dealing with bad professors.

Not everything has to be boxed in by numerics, sometimes simply speaking up and listening is the easiest and best solution.