[Lightfoot]

I thought the light spots was bare metal showing. Now that you mention it, it could also be green paint, but I would think Midnight green was a darker shade. That looks kind of light green. Like Verdoro or lighter.
If it is green paint (original) then that is a good indicator of a solid quarter panel.

Black is the easiest color to reveal flawed body work. That's for sure.
I wouldn't pressure him to wash the car unless his price was to your liking, and you were extra serious about it. I would give it time for him to negotiate down some instead of bugging him further to wash the car. If you wait and he does it on his own, that would be a tip-off that he is serious about selling.
I agree with the others that said $20K is high for a non 4-speed '69.