The short of it is someone has to take responsibility, by having a customer literally sign off on a proof it puts the responsibility in their hands, after that point you can be nice and cut a small discount on a re-run if it will buy some goodwill but it's their responsibility. This has been standard in every print house I've ever worked in or done business with as a designer/customer. The copy shop/small run offset I worked at in college even had that policy, not sure why a large format shop wouldn't.
If you don't have a sign off procedure, it's a clusterfuck and 99 times out of 100 you're going to eat the job or lose the customer.
If you don't have a sign off procedure, it's a clusterfuck and 99 times out of 100 you're going to eat the job or lose the customer.