It's not unheard of to sign a purchase and sale agreement and put a deposit down, sight unseen. Especially, when the boat is in another country. I've done it.I was ready to jump on it. If their ad had been more in order, and the salesman happy to inspire confidence by following through with detailed responses, I might have got a good surveyor, ordered up a captain, and bought sight unseen!
However, I'd never complete the sale, without laying eyes on it. That's insane, unless is highly specialized, well known and you have a very personal reason to trust the players. In my case, my offer was accepted and I booked a flight to attend the survey. Then I rejected the boat and got my deposit back. Good lesson.