Need advice and also a warning.

A lien can only be placed against a vehicle when work or services have been completed on a vehicle and the registered owner refuses to pay. That doesn't apply here - the dispute is over the sale of the vehicle.
That's silly, you think this guy won't claim work was completed and he hasn't been paid? Attorneys are professional liars so everyone involved in the judicial system lies to try and at least stay on even ground. Who ever lies the best wins. Welcome to America.