Below, I've copied a previous answer I provided to a similar question. I hope it helps!

Your best bet would be first to make sure that the book comes from an academic publisher (Oxford, Cambridge, Yale, or any other university press, along with other non-university academic publishers like Palgrave MacMillman and Routledge). Looking only for academic presses can be limiting, though. There are many, many good history books that are published by non-academic presses. Farrar, Strauss, and Giroux normally publishes very good history books, as does Penguin, W.W. Norton, and many others. Besides that, look at the author information in the back flap or the very beginning of the book. Does this person have a PhD (or maybe a Master's) in history or some other advanced degree related to the topic of the book. Or does the author have some practical experience (government job, non-profit work, etc.) with the topic being written? If so, there's a good chance the book will be fairly reliable.

Moreover, read book reviews. See who is writing these reviews, and make sure they are actual experts in the field. For amateur historians without access to academic journals, The New York Review of Books, London Review of Books, The New Republic, and H-Net.org, among others, are great places to read book reviews by academics.

Of course, these are just general rules of thumb, not ideal markers of what makes a book reputable or not. There are many good history books by people with very little professional training in history, and there are also bad books that are published by academic presses. Really the only way to ensure you are reading a credible history book is to be very fluent in the topic you are reading about and knowing who the major authors are. This can only come with a lot of time and experience, something most amateur historians don't want or need. With that being the case, the above suggestions should by and large protect you from most of the bad history books.

Edit: I'll expand with some examples from books that I've pulled from my own bookshelves. These books will be related to my specialty, but the general process of seeing if a book is reputable still applies. As you'll see, it's a pretty simple process.

• Westad, Odd Arne. The Global Cold War: Third World Interventions and the Making of Our Times. Cambridge University Press, 2007.

This one is pretty straightforward. It's from an academic publisher, and I can see from the author description that he is a professor of history at the London School of Economics and Political Science. Furthermore, the book won the Bancroft Prize, an award decided upon by academic historians from Columbia University. This can easily be considered a reputable book.

• Leffler, Melvyn. For the Soul of Mankind: The United States, the Soviet Union, and the Cold War. Hill and Wang, 2007.

This one might be a little bit harder to gauge, but still, it'll be pretty easy to determine that this is a reputable book. The publisher is not an academic press, but I can see from the author bio that he is a professor of history at the University of Virginia who has published extensively on U.S. Cold War foreign policy. Another good, if sometimes superficial, way to gauge a book's credibility is through the blurbs written on the back. All of the blurbs praising this book are from noted historians from top-tier universities. We can easily see that this book is reputable.

• Labunski, Richard. James Madison and the Struggle for the Bill of Rights. Oxford University Press, 2006.

This book's a little bit different. It's published by an academic press, but as the author bio says, the author is a professor of journalism and telecommunications, and has a PhD in political science and a J.D. from Seattle University School of Law. This author, as we can tell, doesn't have a professional background in history. His background in law, though, seems to show that he likely knows what he's talking about in regards to the Bill of Rights. That it is published by an academic press gives it greater reputability. Again, this book will likely follow at least the basic tenets of what makes a good history book.

• Van Linschoten, Alex Strick and Felix Kuehn. An Enemy We Created: The Myth of the Taliban-Al Qaeda Merger in Afghanistan. Oxford University Press, 2013.

This one is also more difficult to gauge, but should still be pretty easy to see that it's reputable as a historical work. The authors are not historians, but have worked as journalists and non-profit workers within Afghanistan for the previous 40 years. It's published by an academic press, and, within the acknowledgements section, we can see that the authors sent drafts to noted academics in the field they are writing about. Again, this book is easily going to be reputable.

• Mann, James. The Rebellion of Ronald Reagan: A History of the End of the Cold War. Viking, 2009.

This one will honestly be difficult to determine if you're unfamiliar with the field, and you will need to dig a little deeper to see if this book is reputable. The author is a journalist, not a professional historian, and the book is not published by an academic press. The blurbs from the back are all from other journalists or government officials. If you're unfamiliar with the author, this is when to look for book reviews for both the book you're looking at and any previous books the author has written. If I were to search for reviews of previous books, I would see that this author has written a couple of history books that are highly praised by professional historians. This book is most likely going to be reputable.

• O'Reilly, Bill. Killing Lincoln: The Shocking Assassination that Changed America Forever. Henry Holt and Co., 2011. (An extreme example, I know).

This book is neither written by a professional historian nor published by an academic press. The blurbs for the book are written by prominent authors of fiction (particularly spy thrillers), and the only thing that the other blurbs from Newsweek and The Christian Science Monitor say is that the book reads like a fiction spy thriller. Certainly not a very ringing endorsement of the author's historical methodology and analysis. To be sure, I can go to some book reviews. I'll see that the book is widely panned by historians and that it was pulled from the shelves of the Lincoln museum due to too many historical inaccuracies. Obviously, a book that should be avoided.

I've tried to give you examples that can account for most of the different types of history books and authors. These are the exact things that I question any time I'm looking for a new book or am thinking of buying a particular book. While these books are mainly from my area of expertise, I hope this gave you a general idea of what questions to ask when looking for new history books.