I did repo's for a couple of years and you are right after a fashion. If the seller sell's the vehicle after he has been advised that it is in repossesion, the financial owners can file with criminal court for a stolen, then pursue both the seller and the buyer to recompense them legal fees and to get the car back. That was one of our last ditch threats. The finance companies just want the car or their money, but if they can get both they will attempt it.
If the person who possesses the vehicle tries to sell it, both he and the buyer will spend time in Prison. It has happened too many times.
As far as the lien, the finance company won't file a lien because they legally own it, they want it back. A lien releases the vehicle into the possessors hands.
Jeff