As others have said, % is rare. You get paid per word. 3 cents per word if you're just starting out. Once you're established you can charge much more.
Ghostwriting is hard to get into because you often can't use your past work as a reference or testimonial. It's the nature of the business and NDAs can be a pain in the ass.
Paranoid Arnold,
We do it because it pays? Contracts go for $25,000 or more. If someone really wants their life story told their way, they'll pay.
Kindle is also creating new opportunities for those just getting started. Granted those jobs don't pay all that much. Still, if you're a proficient writer those $300 deals can be a good income source.
Always, always always get money upfront. If they don't have enough faith to pay half up front by the time they're ready to hire you, why should you have faith in them?
