The biggest problem is objective metrics. Did someone try to make contact when something came up? Were they on time? Did the work get done properly? Did the

The biggest problem is objective metrics. Did someone try to make contact when something came up? Were they on time? Did the work get done properly? Did the provider behave in a professional manner? All of the most important judgments are inherently subjective and biased. This then leads up the chain into the problem of rating the rating reputations of the raters.