Here in Montana, we don't have a license for arborists (more's the pity). There are city business licenses in some areas, but no qualifications required.
For pesticide application you need an applicators license if commercially applying or advising (even if not applying). I recently obtained my Research and Demo Appplicators License specifically so I could perscribe and make written recommendations.
What I want to be able to do is educate people on why they should NOT be using the chemicals so easily obtained and, instead, opt for better cultural practices and organic methods. And yet, if I am making recommendations, technically I needed that license.
Sylvia