This was one of my interests in graduate school for my Library Science degree, so I hope I can answer this satisfactorily. The position of pseudohistory (or pseudoscience, or pseudo-anything) does prompt legitimate debates. In general, there's a few reasons you might see less-than-quality nonfiction in a library.

1. You are right that book sales (or rather, sales + reviews + requests + any number of other factors) influence what books a library acquires. Unless you are in a huge public library system or a large university's library, chances are that the person acquiring books isn't a subject matter expert, and has to rely on metrics to decide what to buy. This means that any given history book that makes the NYT bestseller list has a good shot at making it into your local public library, regardless of what scholars think of it.

2. The American Library Association, which is the professional/academic organization that almost all libraries and librarians in the US are affiliated with to some degree, has a very clear stance on censorship. The Library Bill of Rights says:

"II. Libraries should provide materials and information presenting all points of view on current and historical issues. Materials should not be proscribed or removed because of partisan or doctrinal disapproval."

Of course, there are practical limits to providing every point of view. However, a popular book offering a controversial thesis is perfectly in line with the ethical principles of librarianship. A librarians's goal is not to decide what is truth, but rather to enable people to make their own informed decisions. (As an aside, most libraries will draw the line of "reasonable disagreement" well short of anything that might cause or advocate harm to people)

3. There are legitimate scholarly reasons to include debunked or disproven books in a collection. First, those theories could return to good standing in academia after more evidence is discovered that supports them. Even disregarding that, a huge portion of both scientific and historiographic research depends on figuring out how and why we were wrong in the first place. Something like Gibbon's Decline and Fall of the Roman Empire remains an extremely influential text, even if many of the author's conclusions are not really supported by modern scholarship.

Ultimately, it comes down to the judgment of the library staff responsible for acquiring and maintaining collections. We ask questions like:

"How influential is this idea, even if it's (perceived by me to be) wrong?"

"Do the library's patrons want this book? Will they check it out if it is in the collection?"

"Does this book have other value beyond truth, in its prose, illustrations, history, etc.?"

"Are there any harmful or negative effects including this book in thr collection might have?"

It really is a complicated issue - personally, in that position, I would likely not acquire a book widely regarded as pseudohistory for a public library without some other good reason, but I would also not object to a colleague doing so, and certainly wouldn't try to remove something already in the collection.

If you want to read more about the ethical guidelines professional librarians use to make these types of decisions, check out ALA's web pages on the First Amendment and Censorship or Intellectual Freedom more broadly.

Your post sparked my curiosity enough to check my local library's catalogue for where they've placed Erich Von Däniken. At least in Oslo, Norway, they're not in the history section at all, but in 001.9 / General knowledge, subsection Controversial knowledge. (eg https://deichman.no/utgivelse/p1a6525de54a611a0af625d68cdf0f671).

One aspect I have not yet seen mentioned is librarians' reliance on book reviews and recommended buying lists. For example, there are several publications that review books specifically for librarians: Library Journal, Choice and so on. Many librarians use these reviews as way to evaluate and find newly published books. These are almost always written by librarians, many with special subject matter interest. In addition to that, our buying platforms (no, we don't usually buy our books from Amazon) often have recommended lists of notable books. The one my library uses has the reviews integrated into the buying platform and appends tags such as Research - Recommended or Basic - Essential to some books. A good librarian will not stop there but will also consider the other factors mentioned in the other posts, but it is one more tool in our arsenal. Frankly, I can't be a subject matter expert in all 6 areas I buy books for, but I can rely on other experts to give me information about the books I choose.

Hello, I'm a public librarian for an urban/suburban public library system. I recently served on a committee that made decisions on what book materials to collect for the system and I focused on Technical Services (cataloging, collection development) in graduate school.

I would say that /u/Naternaut gets it right on some of the reasons we collect a writer and pseudohistorian likeGavin Menzies. I also want to post separately to share more about how collection development works for someone in my position. This is just one process, however. We're fortunate that we have time and resources to form committees who can make these decisions.

First, most public libraries have a "Collection Development Policy" that helps guide them in selecting books. Here is one from the Nashville Public Library and here is one from the Denver Public Library. Both read similarly because we generally follow best practices outlined by the American Library Association (ALA), ALA accredited institutions, and we also follow each other as peers.

Both NPL and DPL write about collecting materials to meet the "needs" of the community, but also the "general educational interest, recreational, and entertainment needs of the public" (DPL). A big factor in collecting materials is working with stakeholders (patrons, community partners) to understand what educational needs they have that we can provide. But we also have to know what patrons are reading and talking about in the news or in general discourse. So a lot of what we choose to collect comes down to making something in the public interest accessible. Something not factual may still be in the public interest.

We also have to balance that public interest in present political realities - the fact that some people do not want us to collect certain materials. A few of my colleagues avoid phrases like "book banning" or "Banned Book Week" because it's a term co-opted by any faction to refer to books we don't curate - and part of our job is the curation of books that some factions do not love or want. There's a very real and present danger of choosing certain books. For instance, many people and factions view The 1619 Project: A New Origin Story by Nikole Hannah-Jones as pseudohistory on par with 1421 because it was criticized by credentialed and legit historians. They may select commentary from James Oakes or Nell Irvin Painter to delegitimize 1619, or they may argue that Hannah-Jones is "just a journalist" and isn't a credentialed historian in spite of the work of historians within it. Regardless of how cited or criticized the book is, it's still within the public interest to have that book because everyone is talking about it - it's something people want to reckon with for educational AND critical purposes.

That's why it's important to work with stakeholders is providing a transparent collection development policy letting them know what's guiding this decisions, following professional guidance, and making decisions as a group so that people of different backgrounds and education can evaluate and critique potential items to collect.

Typically for us, a collection development librarian works with a vendor (the major vendor for public libraries being Baker & Taylor) and builds a collection of upcoming titles to evaluate. The committee convenes and researches the collection using information about the book and the author. This includes author information and what they use to credential their work; reviews from Library Journal, Publisher's Weekly, and Kirkus as well as other sources; and interviews or commentary already published. Things we look at for nonfiction and history include credentials; subject interest and whether we have something about the subject interest; and also meeting the demand or the public interest for the book.

If a book has a huge demand in spite of credentials or poor reviews, we may feel that the public interest outweighs the negative qualities of the book. Historians on this subreddit have sharply criticized and lambasted Guns, Germs, & Steel as a source of history or a narrative of how the present came to be. But it was also a well reviewed book by sources that serve the public interest - "The New York Times" called it "an ambitious, highly important book". It would be hard to not collect the book in spite of scholarship against it because people are interested in what information and arguments it imparts.

I do want to say that most of my colleagues and I do choose to critically spend money on credentialed and accepted historical works - pop history or otherwise. It may not be a lot of academic historical works, but I've visited very few libraries that didn't have the well-regarded Oxford History of the United States or books by historians like Jill Lepore, Eric Foner, or Gordon S. Wood. If a historical work wins or receives nominations from public interest book awards like the Pulitzer Prize, then most libraries will collect it if they haven't already.

I would also argue that accountability for what comes into the public interest or discourse originates far more frequently from news media and publishers themselves. An issue for "actual history" in collection is their relative lack of accessibility not just in writing but publishers and pricing and demand because of lack of coverage. It's hard to buy a book no one wants.