Fortunately for me (and him), this has not happened to me. I am very trusting and frequently send money to people for things on CL and other sites. Never been burned. Most people are genuine.
I have however, dealt with people like this in other situations. When I show up at his door with 6 280lb biker friends they usually cough up fast. Not suggesting violence or threats but sometimes you have to take extreme measures. I also have no problem whatsoever putting my neck on the line for the greater good. I'm sorry you have encountered such a cockroach. Someone will sink his ski big-time. Keep on him. Karma always wins buddy!