Re: "You make your money buying the boat, not selling it."
What he was saying was 100% correct. You shop around and purchase a boat at 30%-50% below its real value and when you sell it you can sell it at 20% below its real value and come out ahead. When you purchase at or close to real value and sell it close to real value, (real value being what it will actually bring when sold, not some NADA type value) you will invariably lose money.
That being said you cannot place a value on the joy you get when using it. Anyone who tells you that they are earning a great deal as an amateur buying and selling boats is either a professional boat dealer skirting the dealer laws, or is not being totally honest. I was a partner in a high volume truck and heavy equipment business for over ten years, and I ran into people who fell into those same categories fairly often. While it is possible to purchase cars, trucks, boats, or recreational type vehicles and do work yourself to bring them up to a better condition for sale and make some money, by the time you factor in your time, tools, and other equipment it is far better to just either become a real dealer and do it full time or just count what you are doing as a hobby and not worry so much about the bottom line in dollars and cents. Place the value on the joy of owning the boat and you will do far better, and you will not stress yourself unnecessarily about the money you spend on repairs and maintenance.
Boats require more maintenance than almost any other type of transport vehicle, with the possible exception of aircraft, and the results of a failure in either one are often deadly. A boat as an investment surely better be a cargo ship, because if you are not hauling a tremendous amount of cargo for money you are not going to see a lot of return on that investment.
It is good to learn from your mistakes, but much better to learn from the mistakes of others...