We had a later model, around 88-89, cuddy cabin of the same length. It was a good boat. As stated - condition is key. Pull the cowl and inspect the engine compartment, transom, etc. Check for spongyness in the floor. If it has a wood swim platform like ours ensure the wood is solid and the supports are sound. You may use a hammer, mallet, or block of wood to tap around and listen to the thumps. If you hit a mushy spot you'll know. That may lead to rotted out stringers. This is one reason I won't be looking at fiberglass boats in the near future. That and the primary waters I am in are very rocky (lake of the woods in Ontario/MN).
Check over any wiring you can access. If you can get a peek behind the helm do so. You may find some pretty ugly wiring if someone decided to do a hack job themselves.
Test run it. Not just water muffs on the driveway. Put the boat in the water. Feel it over wakes and listen to it. It should feel solid.
Check the trailer over. Ours had to be rebuilt as one of the front leaf springs broke out of the hangers going down the road. Luckily we weren't on the highway yet, but it canceled our trip out on lake erie that time...