Is it even a good idea?

[akktri.livejournal.com]

I've heard so many stories about people who were offered a commission to do a multi-part, complex or epic commission and had the buyer stiff them. I myself have had two commissions fall through, and both were complicated book illustration projects.
However, I am wondering something. Has anyone actually worked on a successful multi-part, complex or epic project, and had the buyer come through on it? Or is it just a plain bad idea to do them?