I read a great line in Seth’s blog last week. (You know you’ve made it when people can refer to you by just your first name. Although it does help if your first name is Seth rather than Tim).

The line that jumped out at me was: "the best way to make a hit is to build something for the smallest viable audience and make it so good that people tell their peers.”

This is true in our game, too. If you're looking to commercialise your expertise there are three good steps in there.

Narrow your market. Then narrow it again. Get it down to what Seth calls the smallest viable audience. (You may have a few different narrow markets but that's a story for another blog).
Deliver great value. Make it so good that people talk about it. Be exceptional.
Be easy to refer. Make it really clear to your customers that you appreciate them spreading the word, tell them how to do it, be of service to their friends, and say thank you.

Do those three things, and you are well on your way.