For example, if a client approaches me with a rough draft or outline of a book about the mountain dulcimer, I would next want to find out if there are any forums or discussion groups about the mountain dulcimer on the internet. I would then want to know what the rules of those forums had to say about commercial posts. If I would be allowed to make a post promoting the book, I would have an easy way to reach out to mountain dulcimer enthusiasts without spending a bunch of money.
From a sufficiently detailed set of notes or a rough draft, I could probably produce a publishable manuscript working a few hours a day for a month or two- depending on the length of the manuscript, of course. Let's say the total amount of work required added up to a hundred hours. If we ended up selling each book for a ten dollar profit, I would get five dollars for every book. If the book sold as many as two hundred copies, I'd earn ten dollars an hour for my work. It might take a little while for such a niche topic, but it would be fairly reliable. It would be surprising if the book didn't sell at least fifty copies in a year, and at that rate it would take four years to reach my goal. If I can count on earning at least ten dollars an hour, then a project is worth my time. If I can't, then it isn't.