Since it is winter, you should be able to find a boat mechanic to evaluate the condition for a reasonable price. Sometimes during the summer the boat mechanics are so busy it is hard to get the boat scheduled for evaluation in short order. Since you can not do a test drive, I would highly recommend it being evaluated by an mechanic independent of the deal. $35-37k is a lot of investment to be balking over $100-200. Maybe work it out with the owner as far as who eats the if repair costs are over a certain amount. Find out how much it will cost and if someone is available to do it.
So is the reason you can not do a test drive is that the water is actually frozen over or the air temps make it a concern that the block will freeze so fast you will not have the bit of time that it takes to winterize the boat to the point of freeze prevention? It takes less than an hour to winterize (dry block) an MCX and the couple other items (shower, heater) that may need taken care of immediately if they are even present in the boat. You are talking about a major investment... I agree with prior comment - test run is highly advisable. My