Have you ever done a white paper? Marketing materials? A web site for a small catering company?
What do all of these projects have in common? Not only can they be complex, but more importantly, all of these projects can involve an organization's image. Any time you come anywhere near image, you run into the situation that many different people within the organization (the head, the second in command, the marketing people, the lead designer, and more) all want input. And in fact they often should have input. Just not at the expense of the project.
Without the right approach you can get caught in the middle of internal politics and tugs of war. These types of fun can lead to infinite and confusing change requests from many people all at once. If you quoted them a per-project rate, you'll end up making far less per hour than you had expected. Even if you're being paid by the hour, you'll end up miserable because you can't get the project done and the client will probably complain about the bill.
So how do you avoid this? Insist on a single point of contact. This will be the person inside the organization that acts as your interface or buffer zone to everyone else. This insider can handle much of the internal push and pull, whether by mediating a lot of the issues behind the scenes, or pulling together meetings where you can find out more about what the problems are and how you can address them.
Essentially, you make the client provide their own internal wrangler. Along with that, also define who has to sign off at what milestones, and keep those numbers down to a minimum. Ideally, it's the single point of contact that signs off on things as well. Even if internally that means they have to get five people at the company to sign off first before they can do so.
Along with this tactic, also set a specific number of drafts that are included in the quote. One or two is typical. From there, additional changes cost extra.
Doing all of this might feel a bit like micromanaging and being draconian, but really it's just being professional. I'm a big fan of setting expectations up front. When everyone knows how it's going to work, then things go a lot more smoothly. You'll end up much happier, and your clients will too.