Grant i don't believe there are any used jetski's in good condition engine wise as they all cop a floggin, jetski engines are direct drive meaning they run at what ever RPM u hold the throttle, my first jetski was back in 2001 a Seadoo SPX little 85 horse power 2 seater i absolutely cained the ass off of it but i never knew any better and it was fun that is untill i tried to water ski behind it and blew it up
i sent the engine off to a Seadoo dealer on the central coast dealers back than were few and far between from memory there were only one dealer in Sydney at the time Andrew Short Marine
i took my engine to the central coast store not ASM i kept calling up about my engine asking if it had been rebuilt back than they never quoted u on a job it was put the engine in let them tear it down and than they'd give u a quote well i put the engine in and said just fix it, 3 weeks went by not a call 6 weeks went by not a call i waited 11 weeks finally i get a call to say my engine is ready $2800 repair bill
i think the big repair bill was when the water police towed me back to the boat ramp they were towing 2 of us on the ski around 70kph it forced the entire engine to fill with salt water
i had the cash for the repair bill from memory over the time they made me wait i saved some extra cash but i ended up buying a second hand Seadoo HX 720 that was a ex race ski
anyhow IMO if u can't learn to rebuild a jetski by your self than your better off not owning one, they cost an absolute fortune to repair even when making the repairs your self but when u get a shop to do the work the price sky rockets
have only ever owned 2 stroke jetski's and any advice i will give u if u go with a older model like the 2 bangers stick to 2 cylinder engines as the 3rd cylinder on some bigger models doubles the rebuild cost if not more than double