Ck underneath for damage to the hull, ck the prop and ask if it's original, it could be replaced with a cheaper aluminum one. Clean in the hull? Gelcoat shiny? plastics rich and intact? bring a tester and check compression, ask to hear it run for a few minutes, if possible meet at a lake and go for a ride. Look for work done to the engine, paint on bolts chipped? or engine repainted (rebuild)? It's a dice roll buying a running 24 yr old ski, it could crap out first trip to the lake.
Keep in mind, people will lie their ass off, I got tired of catching people in lies looking at the "needs nothing, low hours" skis for a premium. I've bought 2 skis since last Summer and that were trashed and needed significant attention, I basically got them very cheap and I'm doing a resto, which is taking time. Hard for people to lie on a bad non running ski, you get what you get.