I noticed in talking to some current ghostwriters that they were feeling concerned about getting assigned topic they didn't want to do. Nothing porn or whatever - just boring, hard to research topics.
I told them to either:
1. Thank the client for the opportunity and explain that it wasn't a good fit or...
2. Deliver what they originally hired you for and explain that due to the grueling nature of the project's research, they wouldn't be able to do it at that price (charge more).
Here's a tip, too - for the buyers who USE ghostwriters:
If you have a difficult or boring topic that no one seems to want (ie: you're always losing writers after one project), assuming they're not avoiding YOU but the topic, you can do something that alleviates the cancellations:
Gather some research and send it to them with the project. Or, if they come back to you with increased rates, consider doing this. It could be hard copy books (John Reese used to send me about 10-20 books for each project I did for him - and let me keep them), or cut and pasted research from the Internet (however with some writer's you're going to have to STRESS that it's for educating them, only - not rewriting.), or link to some sites or videos or other resources that might make their job quicker.