Sounds to me like he's playing you.
What year Vette is it? What's the inside look like (full interior, etc)? What kind of wheels and tires (street radials, drag radials, E.T. Streets)?
Did you look at his motor? Does he have any spray (NOS lines)?
There's a lot of simple ways to size up a car. The quickest and easiest is by checking the rear tires.