First, and most important, see a lawyer! A few bucks spent on legal advice will seem like a drop in the bucket if you're up against an experienced scam artist. While it is tempting to go off on the guy, you'll only make your position hard to defend. He could be held liable for depreciation or damage to your truck while it was in his care, but he might also have a claim for parts and/or labor before he releases the truck. A legal beagle can save you a lot of grief!
Jerry