I just purchased a Montery boat and it was 15 degrees on the water when I did my sea trial. I would never purchase a boat w/o a seat trial unless your getting a warranty. If I ended up not buying the boat I would have had to pay to re-winterize the boat, but its absolutley worth the risk. Re-winterization is cheaper than a new engine. At a minimum buy a compression test kit ($30) and test the compression your self. Check with the dealer what is should be and all cylinders should be very close......
My opinion, hope it goes well...