Re: "You make your money buying the boat, not selling it."
People who buy a boat want to own a boat. The reasons for doing so vary, but the desire needs to be there. But buying a boat is often like buying a car, wear and tear and the elements break them down and they depreciate. The man I quoted has bought many of both. I think his comment was about reducing your out of pocket costs, not a statement about how to get rich.
Until last night, not one boat we've looked at had an asking price more than its original selling price. The man with the quote is smart enough to know most boats depreciate over time, thus my take on what he meant by the quote.