About 7-8 years ago I got into Generac and became an authorized service dealer, or whatever they call it. IASS is the acronym, I think. I took the training because I didn't want to install a unit I couldn't service. I have probably supplied and installed 20 - 30. Every one was through a current contact. Prior to that, I referred them to a friend/ colleague. This friend/ colleague services hundreds, if not thousands of Generac generators in a 1 or 2 hour radius. He does well at that, with several employees. He does so well that he prefers to just service them, doesn't even want the installs. Ironically I got into the installs BC he didn't have time to install (3) that were lined up for my customers.
While the training was great, and I learned the units inside and out at the time, it was never meant to be a mainstream of my business. (the service, I continue to install some). If you're going to do generator service well, you need to do it every week, if not most days, IMO.
This is for home standby. Commercial generators are a different beast.