The manager smiled, said no with courtesy, and gave good reasons to both of my requests. That's the essence of good customer service - gaining fans regardless of the outcome.
Also, watching this video, I found that the manager only mentioned they weren't allowed to have people behind the counter. He didn't say the source of that rule. However, while in the restaurant, I remember him mentioning the food law as the reason for the refusal, which was the reason when I was refused to make my own sandwich.
I believe the discrepancy between my memory and reality was due to my associating the reason for the current refusal to an earlier one. In another word, at that moment, I didn't hear the Whataburger manager's voice, I heard the Subway employee's words in my head - "no, the food law and government won't allow this". So, did Whataburger refused me because of the government, the company, the store, or the manager himself? Too bad I didn't find out.
1. Great customer services is more about attitude and respect than outcome. If we have to say 'no', say so with genuine smile and a good reason.
2. In negotiation and conversation, the ghost of the past often creeps up without us knowing, causing an automatic association that could be inaccurate, if not detrimental to our success. We need to listen to the other person, not the voice in our own head.