Career Opportunities in Writing (T. Allan Taylor, James Robert Parish, 2006) is a book describing various jobs in writing. On page 101, it lists
Fact Checker Duties: Check the accuracy of manuscripts or other material prior to publication Position Description Publishers of books, periodicals, and reports tend to rely heavily upon the accuracy of their authors, but most publishers have Fact Checkers double-check for errors. … Thus, a Fact Checker helps to guard the reputation of a publisher and its writers. Fact Checkers usually work from a copy of the manuscript and frequently have access to the author's original notes, interview tapes, and other original material. … if an author states that a certain event occurred on a particular date and in a certain place, a Fact Checker must verify all three elements by using such sources as an encyclopedia or specialized biographical dictionaries.
Thus, a fact checker is a person employed by a publisher, and working with its authors and editors to ensure accuracy of books and other materials it publishes. A fact checker does not debate third parties. Magazines and newspapers used to employ multiple fact checkers. It used to be a serious job.
The Fact Checker’s Bible: A Guide to Getting It Right (Sarah Harrison Smith, 2004) is a book explaining ins and outs of this job. Examples:
Fact-checking has a long history in American magazine publishing. The first fact checkers were probably those hired in the early 1920s by Briton Hadden and Henry Luce for their fledgling publication Time, which was founded in 1923. These checkers verified names, dates, and facts and marked news items for writers to use when compiling their stories.
I was a checker at The New Yorker for about five years, and since August 2002 I’ve headed the checking department at The New York Times Magazine. ... Both magazines employ full-time fact checkers who check virtually every word that goes into print.
That was written more than a decade ago. Now these publications decided to stop fact checking their own writing and instead “fact check” their opponents.
Fact-checking protocol will vary from publication to publication, but in general, the author will provide sources of some kind to support all factual assertions.
This has dramatically changed and now writing is checked only to ensure adherence to the party line or predetermined narrative.
Fact checkers who are allowed to do their work to a high standard will almost certainly catch fabrications before they go to press ...
Like the Steele dossier and Russia Hoax.
Fake Fact Checkers
When Google, Facebook, and Microsoft state that they use fact checkers, they are presenting themselves as publishers, even in respect to information received from third parties. Such representation probably overrides the limited protections given to them by the Section 230, but not bring their activities under the protection of the First Amendment.