yup.. exactly: nothing to do with the car. It just sounds like the other person won't pay out and now you're clutching at straws to get the money back.
Fact is, a large number of dealers are dodgy and this is a regular occurance. And like skyline33 is also saying, you get cheap cars for a reason. But that really isn't the point in this case. Still, could have been the best car in the world and you'd still be in this situation right??
You should have definitely reported the incident to the cops and tried to find any witnesses at the time, but may be too late now. If bringing legal action against the 4WD owner (or his insurance company, if he doesn't against him directly) doesn't work.. best thing you can do is take all the items that are still as one piece such as engine, gearbox, diff, etc, and try and sell them. If you add up all the prices of the items separately you might get $8k or something as just parts. Its better than a kick in the head anyhow..