Are there any circumstances under which you should agree to ghost write or re-write a book on a profit split rather than a cash-up-front basis? I would personally do it under only one set of circumstances. If the book in question is written to appeal to an easily definable niche market, and if there is an easy and inexpensive way to appeal to that market, then it might be worth my time to take on that project.

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.