What Guarantees Can You Expect from a Ghostwriter?

The only guarantees a ghostwriter can offer are those elements in the writer's hands. This means that a writer can perhaps guarantee your satisfaction with the writing or your money back (though I don't know if anyone goes that far). But, for the most part, a writer cannot ever guarantee publication, unless you are self-publishing.

A writer is in charge of the writing ONLY unless he/she has agreed to help you in other matters. That means the writing is usually the only area to possibly be guaranteed.

Since I don't know of any ghostwriters that would pay money back after providing work for you (in other words, if you're unhappy with the writing), the best form of a guarantee may be to get samples -- CUSTOM samples, written for your project -- before investing. If a ghostwriter will not provide this kind of sample, you should definitely be able to see other samples - and you should be very comfortable with that writer to trust the work without something done on your project.

And if you are only provided samples from other projects, look for one written in the tone/style you're looking for in your own project so you know the writer can provide what you need. Otherwise, if they want the job, tell them they need to produce something custom with that kind of tone/style. It's the only way you can really feel a guarantee.