My advice would be to bring someone who is disinterested in flying to look at the plane. Tell them to look for dents, dings, ripples in the skins, paint chips, etc. Report them all to you and photograph them w/ a digital camera so you remember.
Also, grab the prop and give it a tug, look for end play in the crank shaft. You should hear a "thunk" when it moves and you want that.
Also, check the attach hinges for the horizontal elevator. Grasp the horizontal fixed part and with the other hand grab the elevator and try to wiggle the elevator at the hinges. This will indicate wear at the bushings. Not something you want to leave uncorrected.
Sample the fuel and look for contamination, also ensure all the sumps dispense fuel and then properly stop the fuel flow.
Next, have your pre-buy mechanic check the torque on the cylinder bolts. Make sure they are tight and stay that way.
All of these things (and a few more) ended up costing us 5 grand after the prebuy and annual was complete and we owned the plane. There are a million things to check to ensure you have a mechanically sound plane, so be sure to get a good, independant mechanic and make him your best friend.
Good luck & let us know how your search turns out.
