They're just trying to mind-fuch you, hoping you don't know any better. They wanted to buy the car for a cheaper price, and were trying to reverse-psych you into it.
I wonder how many '73s they've bought that way. "Oh, it's a '73. I"m sorry, we were deifinitely looking for '74 or newer. '73s have the undesirable body trimmings and whatnot. BUT, if you'd like to sell your '73, we can offer you $xx,xxx. Sorry, that's all we can do.
Sell your car to someone who actually wants it. You said you're not in a hurry.