I can't speak for other agencies, by SSI sends out a survey to all students following their classes in order to get feedback, but it is also used as a sneaky way to catch standards violations. They don't straight up ask "Did your instructor violate our standards?" because students would have no clue, but there are questions about how many students were in the class with you, how many instructors there were, how deep you went during the check out dives, etc., so they can find out if standards were violated. Sure, some students have terrible memories or are just terrible at answering surveys, but instructors also have to keep training records so if a student says that he went to 180 feet on his check out dive, the shop can look up the training record that was filled out by the instructor at the time of the dive and say "Nope, it says they went to 18 feet. Also, that quarry is only 22 feet deep."