If it is the real deal, I'd buy it.
Be careful with the '69 chevelle. Unlike 68 and earlier, there is no way to determine from the vin/trim tag whether it is a real SS unless it is an original orange or yellow car (which were only available on SS).
Be sure the car has proper (and not fake) documentation before you buy it.
Lots of info here:
http://www.chevelles.com/shop/ss_ident.html