Maybe it seems odd to call someone a historian who is not a professor of history giving lectures and writing books.
It’s not odd at all. There is academic history, and there is public history. Not really different things, but broadly different ways of engaging with history.
"Academics tend to think of public history as a field of study, like one of the nearly 300 specialized subjects that the American Historical Association lists when it asks its members to identify their research and teaching interests. More socially engaged historians, on the other hand, consider public history a calling designed "to help people write, create, and understand their own history." Still others believe public history should influence the formulation of public policy. But a majority probably just defines the field by the workplace: academic history, they assume, is practiced within the university, public history elsewhere." (Weible 2008; citation removed)
For the most part, public historians are those who work for museums, corporations, and the like. They are employed as professionals whose job is to do work related to history. If they weren’t so employed, they’d be independent historians.
But there’s some professional angst here, at least among academic historians.
"The question is: if historians in and out of the academy are trained in the same institutions, if they share an educational mission, and if they produce work that holds up to professional scrutiny, then what is the difference between public historians and more traditional ones?" (Weible 2008)
There’s a struggle here. The audience for academic historians is other academic historians. That’s the very essence of peer-reviewed work. On the other hand, the audience for public historians is, commonly, the public.
And there’s the danger. The consumers for whom public history is created are not historians. The result is a kind of history that is market-driven and democratic. There is a risk, then, that it will be less rigorous academically.
"Consider for a moment that most historians know that the Founding Fathers were more influenced by the Enlightenment than by the Bible, that the Holocaust really happened, and that Saddam Hussein never planned the attacks of September 11th. There are, of course, lots of people who understand things differently. Why? Possibly because they are influenced by those who interpret the past more loudly—if less rationally—than others, often on radio, television, and the internet, or in churches, bars, and political campaigns. If we have learned nothing else in recent years, it is that history is very powerful and can be dangerous in the wrong hands, whether in local communities or the nation's capital. It seems that in an idealized marketplace in which everyone is his or her own expert and all ideas are equal, self-proclaimed champions of democracy can legitimize their potentially unlimited authority, not by grounding their truth in objective, scientifically determined facts, but by concocting and selling self-serving histories that play on public fears, prejudices, and greed." (Weible 2008)
I’ve seen a variety of answers over the years, but none of them satisfactory. I tell people that if they don’t have a background in history and historiography, the best way to judge quality is to look for general agreement among historians.
If someone tells you the Merovingian dynasty were descendants of Jesus, it’s easy enough to figure out this is a minority conclusion, and one that’s universally rejected by academic historians. Go ahead and enjoy the story, but don’t sign on to become a True Believer.