I would make it more like a challenge in American football. If you’re not familiar with that, basically NFL coaches get two challenges per game to use on plays where they think the officials got it wrong. If a coach challenges twice and win them both (the call is overturned) they get a third. If they lose a challenge, they also lose a time out.
Let employees “challenge” problematic customers. If the manager agrees that the challenge was appropriate, the employee keeps that challenge. The employees are still limited in how many challenges they get in a certain time period, but it scales with the number of asshole customers they encounter.
