i feel sorry for you but my personal opinion is that as the buyer you must be aware and responsible to check the car, when selling a car owners will never tell you the 100% whole story about the car, even for minor things (unfortunately in your case, major)
this is why everyone usually gets the car checked out by an expert if you cant check it yourself, and revs check etc.
abo bob, from what you are saying there must be different circumstances in relation to money owing on the car, because as far as i understand it if you (unknowingly) buy a car with money owning on it its your problem?