Whom Would You Trust as Most Reliable? Discuss the Credibility

Whom would you trust as most reliable? Discuss the credibility and authority of each individual or group listed with regard to the following issue:
You are looking at a sailboat that you're considering buying, but you've never owned one before and don't know whether you should buy this one.
a. the boat salesman at the marina that owns the boat
b. a boat salesman from another marina
c. a friend who has owned several similar boats
d. a buyer's guide published by a sailing magazine
e. your own appraisal