Can someone put a lein on my vehicle without a legitimate debt?

i recently purchased a vehicle in VA from a small dealership. The car salesman told me that the car was in great condition and nothing wrong with it, i purchased the car with a check and both parties agreed to a balance of $1050 still owed to the dealership and to be paid within the next 2 months. When driving the car back to NC after purchasing it i quickly realized the car is definately not what the dealer told me and there were many many problems that were unmentioned at time of purchase. I called the dealership the next morning and they were understanding that there were these problems and the previous signed balance of $1050 was dropped to $525 to help cover some of the problems that werent mentioned before hand. My question is, am i still liable for the $525 if we never resigned a document stating this, and with more and more problems with the vehicle (unmentioned problems) is this a liability to the dealer for not mentioning these things?