>Ratings measure how good a restaurant is compared to other restaurants in the same class because that is where their patrons' reference frame comes from.

See above, but I find the opposite to be often true. I see reviews for restaurants I am very familiar with, that I know to be excellent and basically the best option for innovative cuisine in a 100 mile radius, which say "Way overpriced small portions". Pretty clear that whoever wrote that review was operating outside their preferred restaurant class.