Not specific to what you should look at (although leaking stanchions would be a red flag
), but if you decide to purchase this boat, it might be worthwhile to let the owner re-commission it. Yes, take a good look at it while it's out of the water, but let the owner do the work to get it back in sailing trim. Otherwise you are stuck having to get the act together before you even can do a sea-trial.
Others may disagree with this advice, but having been "stuck" with the commissioning work myself (including shoveling snow of the deck so we could launch for sea-trial), I would not do it again. You pay for the survey and launching for sea-trial, but the owner should present the boat ready to show and trial. If he/she is an absentee and can't do this for whatever reason, take your hassle off the price of the boat.