> You don't say NO to the client, you say NO to a potential customer before they become the client.

This is critical, and it's fairly easy to recognize potential 'problem clients' when there's still time to escape.

Or just make sure you have an escape clause in your contract. Maybe the last designer actually was an idiot. I've found that if you behave like the doctor (in the article) it's often quite easy to steer the course of projects with even very difficult clients.