Don't forget to look into special license requirements (WDFW, USCG, etc.)! Technically, even a guest bringing along the beer as compensation for the trip constitutes a "passenger for hire," but definitely if you're being paid.
I'm rusty on this state's rules, but how about you full time guides addressing these details?
Special insurance policy too?
Not to forget the "thick skin" protection against all those 'difficult' clients!