Well delamination would be the biggest thing to look for. The good thing about a Glasair though is that it’s a kit and the layups are already done. The wings and fuse are essentially putting two halves together. Now, there’s always the chance of a flaw at the factory and a chance of hidden damage, but rare for a Glasair. I’d be more concerned about a plans built aircraft as far as delam.
Crack in the finish is normal. That’s either the paint or the gel coat beneath that has cracked over time. Even on the Glasair, you’ll see common areas of cracks. I had a so called “fiberglass expert” sand some cracks off the finish because he was concerned about the fiber glass. The fiber glass was fine and he made a mess of sanding off the gel coat.
There is generally a lack of inspection plates on composites but the Glasair in particular isn’t bad. I’ve got two inspection plates on the bottom of each wing. Really not much to look for though. No corrosion to worry about unless it’s controls / hardware. Glasair did a good job of powder coating because mine doesn’t have a speck of rust on the push pull tubes.
There’s cautionary tales about UV damage with composites but again, I’d worry more about plans built. There’s the slight risk on extremely hot ramps, the airframe could get to glass transition temp (Tg). That’s when the resin gets liquified again. If you’ve seen the old Diamond Katanas, they have a temp indicator warning of this condition. Never actually heard of a plane getting into it. Most of your kit planes are built with in a controlled environment and some are autoclave so the odds of getting into Tg are slim.
Outside of all that, I’d just look at the same things you’d look at in a metal aircraft. Airframe wise, just look for any visible damage.
