Whose side are you on?[name that sammich edition -mod edit]
The customer doesn't need to explain to you why they want both subs marked. They just want both subs marked. The subs could be for someone else. It isn't your business. So you thought just one needed to be marked. They asked for both. Do it. There is no need to argue with them unless they are trying to get something free for nothing. I run a restaurant.... I will be firing that employee.