While the performace boat market might be in a recession, triple-engine boats are in a depression. Triples have never been a great idea. The weight and drag disadvantages and increased fuel consumption don't come near to offsetting any performance increases you might see. The same boat with slightly more powerful twins will go faster and burn less fuel. If he buys it, he'll be in the same boat as the current seller if he ever wants out.
Can't help you with the rest of it- other than to say that if he has to own it, a complete survey by a knowledgeable HP surveyor is worth more than a truckload of second-hand info.