My personal trainer wants to launch an unconventional course/ebook but want’s validation first, how would you validate?

My personal trainer has had to cancel my some of my sessions because he’s been getting subsidised clients from Hospitals and GP’s. He’s been doing this for a while and he’s slowly let more of his regular clients go because he can make 4-5x his money. So for obvious reasons I’m not that mad about it.

He mentioned he wanted to start a course or write an eBook on his unconventional methods to getting clients from Doctors, Hospitals and Aged Care Facilities…of course I talked his ear off about it.

How would you presell this prior to building it? I've kinda convinced him he needs validation before sinking time into anything.

Thanks in advance :)