Does it need a lot of explaining? Presumably the workers are in it because they need the money. If a customer hits your rating they're threatening your ability

Does it need a lot of explaining? Presumably the workers are in it because they need the money. If a customer hits your rating they're threatening your ability to make the money you need, so there's no reason not to ding their rating in retaliation if they ding yours. And the other workers don't have a reason to care, you're making their clients more nervous to hand out imperfect scores too.