Look for any water in the ski locker or bilge. Any soft spots in the deck are a deal breaker. Look for faded interior pieces or cracked vinyl as this can indicate the boat was stored outside uncovered. Look in the engine compartment for signs of oil or power steering fluid leaks. Look at the underside of the motor cover/doghouse, and any seat bottoms that are accessible for signs of wet or rotting wood. This also can be an indication of poor care by a previous owner. I'm not familiar with the performance of the 3.0 mercruiser, but I think it may be under powered for a ski boat. It will probably be fine for cruising, but don't expect it to be a hot rod on the water. If it's in good shape mechanically and structurally the current owner should be willing to meet you at a lake to do a sea trial. Do not by it without one. In the end even if all those things check out, I would only offer $2500.00 and only actually pay $3000.00 for it. Remember boats don't appreciate in value based on age like classic cars do. Also ask about service records. A good owner will have records and receipts .
Just my opinion with a rotten glass ski boat in my garage to influence my opinion.
Good luck.