We have them here in Houston. One of them, the slogan on the sides of their trucks is, "All You Do Is Feed The Fish." Cute.
I don't know about fees or duties. I'll bet you could do some Googling (maybe even that slogan) and find a couple of companies' websites, and learn from those.
I'm betting it's as much equipment maintenance as pond maintenance. Filters, clogged pumps, etc., in addition to green water cures, overgrown plants, moving rocks, etc.