It's pretty simple
In addition to location, location, location, as in real estate, it's serendipity. Boats don't rotate like houses do. When we sold our C25, the first prospective new owners went out on a test sail. All was well until haulout, when there were bubbles on the keel. The surveyor said: "No problem, pop 'em, paint over 'em and the boat's great." The wife mistook paint on lead bubbles as hull blisters and freaked out. The next day a dockmate with an Etchells 22 came over, read the survey and listened to the story and bought it. All the printed and internet ads do less, in my experience, than a clean, good looking, well setup boat at a dock with a happy "for sale" sign on it. Figure a reasonable pric that you can accept by negotiating so you and the buyer both feel you got a good deal. Good luck.