The first question I would ask is how they know those are the miles on the car? The car has obviously been repainted, which most cars with just 50k miles don't need repaints. Second, there is wear on the steering wheel at the 11:00 position where someone would hold the wheel for a LOT of miles, and as you expect to see when there's wear at the 11:00 position, the silver trim on the top portion of the driver's door panel is worn, which is indicative of someone who liked to drive with their arm on the top of the panel and hand on the wheel at 11:00. Also the seats have been recovered, something else that's odd for a 50k mile car. I would suspect this car has a lot more than the mileage on the odometer, and should be listed as an Exceeds Mechanical Limits (EML) car.
I would also ask who did the repaint on the car. It looks nice, but all the Road Runner badging is out of place on it. so if they didn't take the effort to get that right it makes you wonder what warts are lurking under that paint.
I agree with 73runner that $7k would be a fair price, but without iron-clad documentation proving the mileage, which I would bet they don't have, I wouldn't pay any more than that. The car is a 318 green/green car, which is the red headed step child of the line. I see some idiots have bid it up to $16k already, which is foolish as I've seen better restored big block cars selling for less.