I have heard that Munich is full of great people and are used to the tourism since so many people go there.
That's probably not wrong. OTOH there are great people all over Germany. Munich isn't special in this regard.
I'm sure the customer-service personnel that you will be in contact with as a tourist in Munich are plenty used to interacting with tourists. It's their job. And you will very likely be treated as a tourist. I'd expect them to speak English to you, just as they would to other foreign tourists who don't speak German (pretty much everyone.) They do tend to speak English well, as a rule, so they have the skills to speak to you unkindly if they wanted to, but that's very unlikely, IMO. As a tourist, however, you are not all that interesting to them, just part of their job, and they aren't likely to explore the political aspects of your home country or ask other probing questions.
I honestly don't know why people worry if some European clerk or waiter is less than polite. Service personnel can of course have moments when they might seem or might be impatient or impolite, whether that happens in New York or Munich. If that happens, don't jump to the shaky conclusion that you've been singled out for this treatment because you are American. More likely, you were just the nearest human target for the person's unhappy moment to be shared with.