What betrayed the car image (to me) wasn't the car itself. There's something about the iron fence behind that doesn't track. Too clean, too specular, or something. Maybe comped in from a separate layer at the wrong focal length or plane.
There's different things about the BMW that give it away. If you look closely at the paint, there's no orange peel to it. Also, the front license plate makes you go, "wait a minute..." If you go to the BMW website, the 2nd still gives away more clues. Look at the BMW logo on the trunk, the rear license plate, and the tires. Tires wouldn't have that much detail in a real photograph.