As with any boat, look for water penetration/staining/instrusion into the cabin. Most notably around port holes or other areas where access has been created from topside (wiper blades, mounting brackets, etc).
A couple other items of note:
1) How do the gray water systems work their way out of the boat? To a common collector in the floor, then pumped out, or do things like the sink go straight overboard? You'll want them to to overboard.
2) Look for Cabinetry movement/flex. A sign of a hard run boat is if the cabinetry is loose in areas, you see signs of uneven or unexpected wear, or misalignment.
3) Canvas. What kind of shape is the support poles, the canvas, the eisenglass panels?
4) Seats and Vinyl - this would be harder to replace. Pink mold? Rips, tears stains?
5) Engines and outdrives -- a good mechanic will help you out here. Do the drives need to be refinished or replaced. Drives, unless well maintained, start to need attention by the 10 year mark. obviously look for service records on the motor and get a compression test done.
7) Steering -- if the boat isn't used regularly, this can be an area where you'll want to make sure everything is smooth and tight
Check the pooper. All systems go? It's a dirty mess to deal with any situations with the blackwater plumbing9) If it's an in water boat -- look for hull blistering
10) Various electronics -- since all of this is most easily replaced, I tend to not complain about what is there -- just as long as it appears to work.