Need advice and also a warning.

What @roccodart440 said about requesting a "civil standby" from the police. If that fails, you can file a small claims case for up to $10,000 in damages, and the filing fee is only about $50. The key part is having the summons personally served on the guy by a process server - that will cost you anywhere from $75 - $200 or more, depending on how slippery the guy is. You don't really want to go to court - the lawsuit is mainly to get the guy's attention and persuade him that he needs to deal fairly with you and return your property promptly.

What damages does the OP have to sue for? Does he have a contract that was broken? The only thing I see is if the title he gave him doesn't match the car. The rest is just typical "not happy with the progress" BS that happens in most shops. A judge won't give him a dime.