Re: lien sale
I can't believe some of these responses are coming from actual licensed attorneys; what a shame.
Anyhow, here's what you need to do; first find out if the lien sale did occur. If so, was the title transferred? You can find that out from the DMV. If the title is still with the bank, then the lien sale didn't take place because the bank would have stepped in to protect their interest.
Also, you should have received a notice of lien sale. If you were not informed, then you may have the right to set aside the sale. The fact that the shop owner is driving the car does not seem kosher. More like he misappropriated your vehicle.
Contact the finance company and find out if they are aware of it. If the car is not sold on a proper lien sale, then you have the right to recover it by any means necessary, including taking it back if you have the keys or hiring a repo guy. You are still considered the legal/beneficial owner of the car. As for the $ owed to the shop owner, at $588 per month, you do the math. He already got his $ back.
Lastly, you may stop paying the payments and the finance company will repo it; but they will pursue you for the deficiency and it'll mess up your credit.
Good luck.