PFM, can you enter a "professional zone" while you are dealing with the guests at work? I always did this. I was in my work role and I kept it seperate from my personal feelings. You are right, your job is to satisfy your customers. It is hard to deal with angry people. I did learn how to do it. I learned by figuring out what scared me about angry people and worked on that. Now I get calm when others are angry. (I worked on making myself relax in the response to it and now it is a reflex).

There are valid reasons why you feel too weak to say no. If you were abused, you probably get triggered back in time and your feelings of powerlessness come back full force. When I got triggered I would tell myself in that moment that the feelings are from long ago and today is a different time and I am safe. It also helps to work through those past incidences that get triggered up in therapy.