To begin with I doubt you will receive too many replies on this delicate subject. Before you start calculating a fee you would be best to check into state regulations for doing commercial pesticide application, even if you are only mixing coffee with water to spray.

In many states the requirements for commercial applicators are extensive. You may need to take courses and obtain a lisence. A liability insurance policy is also a good idea, if not mandated by your state. It may sound like a joke but you may also want to form a LLC and keep your investments secure aside from the business. We're in a lawsuit crazy country and San Francisco is likely the epicenter.

States differ in their requirements for commercial pesticide application. Call your extension office for information regarding the laws in California. Be sure to tell them that the product is an herbal (and oil) based insecticide.

Whether you charge extra or not depends upon how you've set up your billing program and how your contracts read. Most contracts that I've ever seen (and I've helped many companies forumulate their contracts) include a once or twice per year treatment of some kind in their contact agreement, and charge accordingly.

If you don't think that the need will come up very often, then creating a small list of 'add-on' tasks is a good idea.

By the way, what is your experience with this particular product? I'm very interested in knowing what kinds of pests you've used it on and the results that you've had.

Thanks for the responses.
I am a very small operation, so I think the list of "add on tasks" would suit me very well.
My experience thus far with the bioganic has been tremendous sucess on lots of mature Huchera with nasty thrips infestion. I also used it on a Rhodie with thrips and it bounced back well.
The best part is the product actually smells GOOD, due to the clove and wintergreen oils!