Keep It Clean. They say cleanliness is next to godliness…well, a clean boat is, too. A documented engine service record is worth its weight in fiberglass. Copies of yard bills for simple stuff like bottom cleaning, changing zincs, and hull waxing help, too. Be meticulous with the interior upholstery, carpeting, galley, and head fixtures. A dirty or poorly maintained boat could chop thousands off your sale price.