Cheap clients

So I've got the gig lined up with my client to play live, rehearsals are scheduled, and everything seems to be going great! Then, I ask about how much my client planned on paying me for the gig, and I'm suddenly not needed. I encounter this now and again because I'm freelance as opposed to being part of a band, but everytime it happens it pisses me off!!
If these people wanted a plumber to come out to their home, they wouldn't try to stiff the plumber after their toilet was working. Why do they want to stiff pro musicians that they chose to hire for a gig the instant that payment is mentioned? I'm not saying that I'm the cat's meow on bass, but I know that I've got talent, and I'm not going to work for free!
I take responsibility for not discussing my payment arrangements ahead of time, but since I've worked with this client before on a gig that was free, and they told me future gigs would be paid gigs, I assumed that they understood payment would be due... I guess that's what happens when you assume, huh?!?! I make it a point to ALWAYS discuss what I expect for payment, and this time assuming got me no gig and no money... I'm not going to make this mistake again.
Have you guys ever had a chump stiff you for a gig or cancel when you asked for payment? Tell us about it.

I take responsibility for not discussing my payment arrangements ahead of time, but since I've worked with this client before on a gig that was free, and they told me future gigs would be paid gigs, I assumed that they understood payment would be due... I guess that's what happens when you assume, huh?!?! I make it a point to ALWAYS discuss what I expect for payment, and this time assuming got me no gig and no money... I'm not going to make this mistake again.
Have you guys ever had a chump stiff you for a gig or cancel when you asked for payment? Tell us about it.