I don't do a ton of contract work, so I don't have much experience with difficult clients. I'm curious as to how everyone else deals with them.
In particular, I currently have a client I was doing some regular work for for around three months. It was all contract work, but I was working as an employee (no papers signed, just a verbal agreement).
Fast forward three months and I quit. I wrap up what I'm working on, send in a final invoice for the little work I was owed for ($400), and went our separate ways.
Fast forward another month. I had been told on four separate occasions "I'm sending your payment {as we speak|tonight|tomorrow|today}". He threatened to sue me five separate times for things that even a childs imagination would have difficulty coming up with. Every time I contact them it bounces between "I'm going to sue you" and "I'll send your payment right away". The threats of being sued are comical, but I've heard stories that he's not afraid to "make stuff up" if needed (while working there I witnessed first hand him faking documents for a mortgage).
$400 isn't a ton of money, and I'm pursuing it more out of principle than all else (he's done this to past contract workers and gotten away with it). At what point do you generally give up and write it off?
http://vimeo.com/22053820
As for me, In the past when dealing with smaller clients I always get some money up front (usually 50%) to "cover costs" along the way. In your case it's difficult to justify too much time chasing down $400 so you might be better off thinking about that as money spent on learning to be a contractor and quickly move on to the next job.