When shopping for a used car, tell the owner that before buying it you'll take it to a mechanic to inspect it. After shilling out $100 bucks or so, if the mechanic doesn't find any problem you'll buy it. But if he finds a problem with it, you'll tell everybody you know not to buy the car. Tell the owner that proposal before you take it to the mechanic, so he knows the good and bad before you spend money to inspect it. But before you spend money for the inspection if the owner tells you straight up that it's a bad car with problems, then you'll keep hush hush about the car having problems.
It's amazing how many people will tell you the truth about a car when you give them that ultimatum.
Also, call your insurer and ask them about rates for the car.