As Drew said, check that top. If the tonneau cover chatters at all, you probably need a tonneau motor. $150 for a motor, $20 for a new kit, usually $100-$200 for someone with a Tech II to reset if you need that (careful update would avoid it). Probably $1000 at a dealer or indy, but really only what I listed. Use it to negotiate if it has that issue.
Check the top fabric closely for any tears or rips. A replacement used is lots of labor and new is $$$. ASk about leaks (the answer doesn't count, it will be "none" most of the time, it's the length of the pause before he says "no leaks").
Make sure the metal where the rear shocks attach at the top of the wheel arch is solid. They can rust through in your area. I'd poke hard with an awl around the rubber mount.
Ask what upgrades have been done to the suspension. The upgrade mentioned above would be nice, along with springs and Koni or Bilstein shocks.
A/C will be a little hard to test this time of year but do what you can.
As with all these cars, look for vibration under acceleration, up a hill, on the highway, 55 to 65 ish.