And so combining the suggestions from Coury and Randy...don't let bad designs out the door.
In essence, you promise things to your customer. What do you do to ensure the bad stuff doesn't reach your customer? If you realize that a design is flawed, what do you do?
If you have a generic design that goes to multiple customers and realize that it is flawed, you then to have a process for dealing with this situation.
Your product is a service, but the intent is the same. You need a procedure for outlining how you control nonconforming service.