If I were looking for a used vehicle, I would look at the car rentals or dealers who have cars coming off lease. When we bought Melanie's Grand Prix, we checked out a lot of Hertz, Budget and Enterprise sales offices. They usually take good care of their rental vehicles, and replace them based upon a mileage or time setpoint, whichever comes first.
We were specifically looking for a Grand Prix, but most of the rentals only had super charged ones, and with a performance engine, you could probably expect the renters to dog them. We found a dealer that had just gotten one back from lease. Two years old, just under 24,000 miles. It was very well taken care of, had all the dealer service records, and we got a MSRP $25000 car for $14000. The dealer replaced brakes and tires and did a full service on it before turning it over to us.