Agreed - Best part is that he definitely knows the truth about the boat now but the listing stays the same. And although thanks to Shaun we all know about this boat the 'next guy' that calls on that boat will not see this coming.
A couple of other things mentioned and some not perhaps mentioned as ways to avoid this type outcome.
1. Beaten to death, but still worth mentioning, buyer's broker.
2. Surveyor with agreement to stop the moment he determines it has serious issues.
3. Require current photos to be taken, giving specifically what you want. Require some close up shots.
4. If it's distant, engage someone there to go check it out. If it's someone you know, that's great, but, if not, someone from a local boatyard or marina. Pay them $100 or $150 to go take a few photos with their phone and look at it and give you their first impression.
5. Ask some piercing questions of the broker. How long has it been on the market? Have you personally seen it and, if so, when? How many others have looked at it? How many made offers subject to surveys and then walked? What problems were pointed out on any surveys? There are certain things brokers may not have to disclose, but when asked, they definitely must. Why hasn't the boat sold? What have people said to you? What offers, if any, has the owner turned down? If a boat is listed for $100k but you'd never pay more than $80k for it and the owner has recently said no to $95k, then no need to continue. One thing a buyer's broker does is asks the right questions of the other broker on a distant boat. I know one broker who will not even move on a boat with her customer, until she is furnished with current photos she requests from the selling broker.
6. This one is even more radical. A disclosure sheet for the seller. It's become the norm and state law in many states on real estate. It's a detailed list of all parts of the house, all appliances, all rooms, plumbing, HVAC, and the seller must answer either they're in good condition or poor or they don't know.
7. Communicate in writing in addition to orally. If the broker tells you some things, send him an email back to confirm and for him to verify you understood him correctly. Build a paper trail. It also helps make sure you don't misinterpret.