Brent-
I've never heard of someone purchasing the diagnosic cables and disc/program and doing their own analysis on an engine being considered for purchase, but it is a marvelous idea.
You might consider talking to a specific nearby dealer to the motor and see what they would want to perform the diagnostic analysis with their equipment. They would be an independent third party to evaluate the motor.
Might be cheaper than buying your own, although I don't know what that equipment and program cost. Actually, I'm a bit surprised they're for sale to the public.
Why not work out a deal with the seller and including the diagnostic cost of the dealer doing the work. Include it in the price. The owner pays the fee up front. If the motor passes, you'll buy the boat for the agreed upon price, which includes the testing.
If the motor fails, he pays for the testing, you don't buy the boat/motor/deal.
A Fail/Safe Purchase Plan, so to speak.
Joe. :teeth :thup