Come on.
If you're doing a prebuy with a low time guy, or someone who isn't in the industry, go over EVERYTHING, logs, ADs, inspection panels, test flight against book numbers, as well as verifying all instruments work as advertised, go over what he is paying for the plane and let him know what he's looking at compared to the market.
"Joe, she's as advertised and it probably worth a little more than you're paying, good find!"
Or
"Man Joe, sorry you wasted your money, this thing is MAYBE worth 10k, no way on earth I would give him 40k for it, getting this plane up to standard you'd probably pay off my mortgage by the time we had her straight".
If you're too weak to let someone FULLY know where they stand, please don't offer to do prebuys.