I would suggest a test drive and/or test ski/board behind the boat. I would also try and do this with the boat 'cold' as in not started before you arrive. Look/listen for the obvious 'bad signs' - hard starting, excess smoking, water in the bilge after running, temp should stay between 140-180 depending upon t'stat, listen for strange noises, etc. Compression test wouldn't hurt, but with no obvious signs of trouble on a good test drive not sure I'd demand it. I would also suggest inspecting the running gear - tracking fins, rudder, shaft and condition of the hull in general. Any signs of damage, bent fins, hull cracking (including spider cracks), or gel coat repair I'd be worried.
That boat is missing the rear decals - seems odd for everything else to be so pristine. Can't tell but also looks to have pinstripe on side removed(between gel colors).
IMO - these boats are bullet-proof, pretty simple machines. If it appears to be in good mechanical condition, and a test drive checks out - you like the boat, go for it. I'd rather spend $6800 on a boat I can enjoy now. Be sure and check the condition of the tires. Lots of stories on here on tire blowouts on low-mileage tires. Wheel bearings, and all the usual trailer things should be inspected as well. My boat has a single axle trailer, the tandem might be worth a little more too, not sure. If the test drive throws up some red flags either delve further into the issues and negotiate the price or walk away, there are lots of good MC out there! Good Luck!
1989 ProStar 190 Power Slot
Somewhere between SML and LKG