Carfax really is almost worthless. Sure, black marks on the car's history can alert you to issues, but what about the stuff the Carfax is missing? A few years back my wife bought a year old Acura TSX from Carmax. Two days after the car is home I'm under it to change the oil/filter, and I find lots of damage. Both front and rear bumpers have big cracks not visible from the outside, and there's paint overspray (red, so it's real obvious) all over the inside of the wheels/tires, the tray under the engine, the gas tank, and the exhaust. Front airbag sensor was also disconnected, and some sort of non-OEM black plastic piece was plugged into the harness in its place. Well, that car had a squeaky clean Carfax, and Carmax had also "certified" it was a clean car. Returned the car that night (a busy Friday) and made sure all the customers there got a good idea what the situation was. Drove by Carmax the following week, and the car was back on the lot.