Did your customer get affected because of:
a wrong delivery
a wrong communication
poor customer service
Fire the cause of the problem. If you think this is too radical, consider this. ‘If you think you are in any way a reason for this, fire yourself first.’
What happens when you decide to have zero tolerance? Do you think it will impact your business in the positive way or otherwise?
Side Note: It might be hard to believe to have such a policy. If you have the intent, the start is always right. When you start right, you won’t find the need for such a policy.