I hope I haven't made a similarly disdainful comment about people who prefer to be treated informally when served. I certainly don't disdain those who have that preference.

In almost all cultures (except, judging from the perfect random sampling here, the United States of America and perhaps Australia) it is respectful and courteous, a sign of normal good manners, to address people you're serving by surname. If they are more comfortable being addressed by first name, they will say "Please, call me Adam!" and everyone concerned is comfortable and accomodated.

To ask someone how to address them is impolite, because it is uncomfortable for the respondent who prefers surnames. There is a well-established, perfectly polite, worldwide protocol for resolving this problem in all situations. It always works and never fails. There is no need to reinvent or start from scratch. See previous paragraph for the answer.

My impression is that American has already established its practice in this area, and that the OP's experience is an outlier. Or is The New American "arriving"?

I have invariably been addressed by surname when communicating with AA employees. I like this.