Depends on what the deal was.
We talking about someone that was supposed to do some work for you?
Or we talking about someone that was supposed to sell you some parts?

how much "business" does this shmuck do? One time thing, or is this frequent.

if you want his 2 cents, then post it somewhere you know he'll see it.
If it needs to be exposed because you know you're not the only one, then post that shit everywhere. Hell, even get on craigslist about it.
I'm pretty crazy when it comes to that kind of shit, especially if it was a significant amount of money, I'd be in the for sale forums, the lounge, the tech section, general car chat, I'd link it in pit road. do a search to see where else he posts and post that shit in those sections too. Make a few craigslist posts about it. back when myspace was cool, I'd spam they guy's myspace, and their friends myspace. Do the same thing with facebook, but if he has his shit on private, you can just fill his in box with links to all your threads and messages about how you appreciate the cooperation.