with no water test here's what i'd do...
all these things will reduce the value somewhat... the 95 xp 720 is nothing special, its a 1,000 ski all day long in good condition all the items below reduce the price, somewhat.. here's a list and some ballparks on how much you should deduct (not how much it will cost to fix, just how much it devalues the ski, IMO)
check over the hull inside and out very carefully, any fiberglass repairs or missing rubber?
condition of the traction mats. -50
check for grey fuel lines (bad) -75
compression test (-300 if below 140)
inside of hull, how dirty is it... -20
does every gauge work ? -40
engine, is paint flaking, peeling (signs of salt) -50
do all cables appear to work properly and look good, no fraying -50
not sure if this has vts but i'd check that as well -50
are grips or handlebar pad all worn out. -25
find out what oil he used and actually see the can of oil he used
shine a flashlight into the impeller, how does the prop look, good/bad, wear ring as well -50
any rust inside on things like the pto motormount bracket -20
does the engine wiggle (motormount issues) -30
i'd even like to take a rave off and inspect the cyl's thru the hole with a flashlight.
if all that passes your eye test, then its worth buying... i personally wouldn't pay more than $800 and i'd be looking for an excuse to nudge it down to that level, but i'm a cheap bastard, don't like 720's, and ski's are 15% less here in FL.
assuming you buy it, think long and hard as to whether or not you want to run it "as is" , but i'm always leery of buying used and just throwing it in the lake keeping your fingers crossed. I'd prefer that you inspect the inside of the engine but that might not be feasible, since your OP indicates that your not a seasoned wrencher else you wouldn't ask the question, but at the least, pull the raves and inspect the pistons, maybe pull the head and inspect the cyl's