This is for the freelancers.
In my past life as a full-time employee, I was involved in hiring and interviewed a good number of developers. I learned that it was much more valuable to see a developer work through a problem, however small, than to talk about experience, etc.
Now I'm working as a freelancer/consultant. One of the nicer things is the freedom to choose what I want to work on. But now, a few years in, I've learned (the hard way) that some clients are not worth the money. They can be fickle, unreasonable, demanding, and difficult to work with in a very demoralizing way.
So I've been wondering: is there a better way to "interview" clients? Obviously any method would have to be subtle, as the client probably isn't expecting to be tested. But is there an analogue to "FizzBuzz" that will tell me whether I should sign on, or back away slowly?