Hi, looking at a Sun Fizz, eh? Ours was one of the first, and was built in 1981, so you're looking at a boat that's close to 30 years old. Unless they changed the build over the years it was offered, it's a solid GRP hull, cored deck. I would say that a boat of that age is going to have had any material defects show up long before now. So in general, you probably should be looking for signs of accident, excessive trauma, or inadequate maintenance. Also, I'm sure that the owners made some modifications of their own, so those might need to be looked at more closely.
The keel is cast iron. That would be something to look very closely at, as well as the keel bolts. We had a lot of problems with rust from the keel until we had it completely sandblasted and primed with a 2-part epoxy. If there's rust, you might notice it under water, but possibly not, but if it hasn't been finished properly you'll see it when it's hauled. I'd say, though, that except for the keel bolts, I can't imagine any problem with the keel that would not have occurred long before this.
Keel bolts were not a problem with our boat, but it's always something to look at carefully on an older boat.
We had a minor problem with a leak in the deck quite near the nav station - finding an overhead leak is a challenge, be it in a boat or the roof of a house. With the head liner removed one can see any compromised core because it will look black under the resin. This is an issue with all balsa-cored GRB, not simply a Jeanneau's, and would be found by a competent surveyor, since they look for that problem.
Otherwise, I would look over the deck to see if there are any stress cracks in the gelcoat (radiating spider-web cracks, for example). Since the non-skid is molded in - I loved the non-skid on the boat - any repairs to the deck might be very obvious since the waffle pattern in that area would not be there.
We were obsessive about zincs to guard against electrolysis. Because of the iron keel one must be sure the keel zincs are inspected regularly. How carefully did the owners look at, and replace the keel zincs.
What kind of engine? Salt-water cooled or fresh-water cooled?
Otherwise, you might find that the Sun Fizz has the deepest lazarettes you've ever seen (I called them the mother-in-law cabins), and good storage everywhere. We only had one of the two heads installed, the aft head was never installed and we used that as our radio room and rope locker.
If it had cork lining in the heads, look for rot behind that - the only other issue we had, and partly (mostly) our fault.
In general for any boat, some comments.
All boats of that age might have hidden rot someplace - hull stringers, support for windlasses, winches, etc. How old is the rigging? Ours was a tall fractional rig with running backstays - a bit more work than a masthead forestay and shorter mast with proportionately smaller mainsail. The age of the sails might be a concern, again a surveyor would be most helpful there.
I loved our boat. I thought that the aft quarter berths were the most comfortable berth in any kind of weather, any angle of heel. And only a shout away from the person on watch.
Keep us informed of your progress. We all love to talk about boats, even when they're not ours.
You can look at some of our pictures of the gear, changes, work on the boat Watermelon Gear