The GM closed auto auctions are nothing to fear in general. Many GM program vehicles are moved through them and are perfectly fine. My inlaws buy all their vehicles that way. But, like mentioned here, they always run all the service records and do whatever checking they can first, just to make sure what they are getting.
My daughter bought her G6 that way with help from her FIL and is very happy.
As the one you are interested in is a GM BuyBack, I would suggest extra homework until you understand what that was all about. Or find another one.
Mike: 1997 SE w/ 183K, aka White Horse
, Gutted Airbox w/K&N, drilled 180* t-stat, tint all around, clear corners w/SilverStars, "PONTIAC" light up tail, PEMs, NGK TR55s