Well since the seller isn't willing to let you water test the boat, the numbers above don't mean anything...I'd be leery of buying a boat without a water test...you never know what you're getting.
With that said, they do seem to be low on the price, so if you can do a compression test and run the motor with a hose hooked up for cooling (do not run it too long on the hose) and crawl underneath the boat to see the condition of the impeller and look in the backside of the jet nozzle to see what the stator vanes look like and that all checks out...then it may be a good deal?
To do a compression test you'll need a compression tester (may be able to rent/borrow one from a local auto parts store). To perform the compression test you'll remove all of the spark plugs, install the compression tester to each cylinder (threads into the spark plug hole) and crank the engine over with the throttle wide-open (the boat shifter will need to be in the neutral position to crank and you'll manually need to hold the throttle plates open while cranking)...after a minimum of four compression strokes record the highest reading for each cylinder...a good condition motor should be 120 psi or greater...a marginal motor will be above 100 psi...you should not see any variation between cylinders of 15 psi or greater, if so there is something wrong with the cylinder that is lower by 15 psi or greater...