Marking the valve stem location is just fine... I never said anything about that.
What I said was that if the shop tries to put the wheel back in service without re-balancing, it's a poor practice. In fairness, I should have said 'checking balance' instead of 're-balancing' but the idea is still the same.
Yes, you're right about checking the balance after remounting in the same position. At the shop I worked at in high school, it was SOP to mark the valve stem and the wheel weight locations on the sidewall and put them all back in the same spot and then at least check the balance when patching a tire. I agree that it's something a well run shop would do instead of trying to charge the customer for balancing on top of the charge for patching.