Kito's list is good. Obviously, condition of the hull and deck are very important - look for any major cracks or areas of past damage repair, especially on the bow or on the widest part of the hull, where damage from docking accidents are most likely. Make sure the bow eye is good and strong, and doesn't show evidence of past damage / repair. Check the area of the mast step for evidence of softness or leakage, and beneath it, check the compression post - especially earlier wooden ones, for condition / soundness. Outboard motors are expensive to repair or purchase. If it comes with one, check that it starts and runs well, shifts in and out of gear easily, and stays in gear when pushed, and that it has a good, steady, strong discharge of cooling water. Plan on replacing the water pump impeller if it's not been replaced in the last 3-years. Trailers can also be a money pit - they seem so simple; but, bearings, brakes, and tires can add up very fast - some people are surprised to find that the trailer needed repairs that cost more than the boat. If you plan on trailering the boat, make sure it has good, bias ply, "ST" (special trailer) tires, no more than 5-years old or so. Check the overall condition of the keel for excessive corrosion (most are cast iron, so they can rust), the keel cable (broken strands can be felt when raising or lowering the keels - wear leather gloves), and the keel winch - the clutch brake should hold the weight of the keel without slipping. Lastly, for me at least, electrical problems are a major pain to run-down and repair. Test the lighting - bow light, stern light, anchor light, cabin lights.
Obviously, if you have both strong mechanical skills and lots of time available, you can make necessary repairs pretty inexpensively. Over wise, take your time and by the best boat for your money - eyes wide open. C-22s are sturdy, simple, and forgiving. Replacement parts are widely available at very affordable prices. There isn't much that can't be fixed given time and money. You know best your own appetite for do-it yourself projects, and the time and money needed for them. Know what you're getting into.
Some say there are two kinds of boat owners - those who sail their boats and those who work on them. There may be some truth to that. As for me, I prefer the sailing and would willingly spend a little more for a boat that needs less work.
All the best, and I do hope you join the community of C-22 owners. Great boats, great people.