It can really vary from place to place, as well as where the person serving you is from. When I have been in customer service, I, like most people around here, don't really use sir or ma'am often. However, some do. I also notice that some people from, say India, at stores would call everyone "sir" no matter your gender.
Among women, dude is used a lot -- it has no real gender here. *shrugs* also, even a group of women will be called "guys." Examples: "What's up dude?" (A woman to another woman). And, "Are you guys ready to order?" A waitress talking to a group of women at a restaurant. Ladies, and girls will also be used, but guys is also just as common, especially if you have more than one gender.
I've seen folks in the trans community freak out and flip out at a store (or, afterward) when someone says sir, dude, or guys. It's not always an indicator. Sometimes, I think folks in the trans-community are overly sensitive and overly paranoid. And, if you're always thinking like that you will draw attention to yourself. Just be yourself, and don't worry what some guy at a store or restaurant says -- they don't matter and aren't worth destroying your self-confidence over.