Trust the numbers not the owner. Check and make sure the vin plates match.

Question is, do you care if it's original? If you want an original car, or the owner is looking for high $ you'll want to pass it up. But if it looks nice, decent price, and you just want to enjoy driving the car, don't pass it up just because the color isn't right, but one important thing to consider though is this..

If the stuff that's easy to tell is not correct, what about the rest? Are you paying for a 400 that really was a 350 with a new engine and hood? Speaking from painful experience, your best bet in this case is send the vin number to Pontiac Historic Services and have them run the numbers for the original build. It's $45 well spent considering what you could overspend on an incorrect car.

By any chance are you located in the Detroit area?