Great rundown on the clientele from "Big Al" Ewald (leave it to a tour guide to not be able to ditch a nickname, even for an newspaper article) on being a Double-Decker guide in DC. Seems pretty similar to NYC, other than two things
1) He seems to give Euro tourists - who are insufferable for wholly different reasons than Americans - a bit too much of a pass in my experience.
2) He can't talk politics at all! The NYC tourist business might have its drawbacks, but for the most part as long as you don't curse out the customer's children, you're pretty much given the run of your own mouth. It's pretty much the only thing that saves your sanity.