Jim, I have very little experience buying boats, I've bought two used and one new over the years and they were simple straight forward and easy. I've never sold a boat. By the time I'm done with them, no one would buy them.
I suspect, you are just having a run of bad luck. Scammers abound, on both sides of the equation. But also, people are busy, distracted and sometimes lost in outside social and financial commitments that make it hard to concentrate on the secondary business of selling their boat.
I've called people about jobs from putting a new roof on my house to installing bathroom tile and doing custom art for me and had them never return my calls. I'm sorry to say, I've done it myself to others calling or emailing me about my work. Sometimes it just takes persistence. 90 percent of the time I get stressed about why this guy didn't call me back or that guy didn't return my emails, I eventually learn it had nothing to do with me and the guy was just as stressed and concerned about it as I was.
Good luck. I know you'll end up with the boat that is just perfect for you. Fate sometimes intervenes and it's usually for the best.
-Will