How do libraries handle it?
When I was about eleven, I discovered that my local library had a copy of Immanuel Velikovsky's "Worlds in Collision" shelved among the science books. I went to the librarian full of indignation, demanding that they reshelve it under "science fiction." The librarian somehow calmed me down... and the book stayed where it was.
Well, I'm older. (And to tell the truth the geologists seems to be a lot less uniformitarian than they used to be. Asteroids extinguishing the dinosaurs? Well, OK. But I still don't think the fall of manna that saved the Israelites resulted from the earth passing through a comet's tail.)
Anyway, it seems to me that librarians must deal with this sort of thing all the time. And the many public libraries that use the Dewey Decimal system can't just fall back on the Library of Congress. Although perhaps there's some central authority that recommends Dewey classifications. But in any case, someone has to decide whether Velikovsky is science or science fiction. Who does? and how?