Selectors have to Be Both Intelligent and Trained
Credible information sources are identified in 2021 the way they always have been. One should be sure that materials selectors are versed in the notions of:
1. Authority--Reliable information sources are signed/attributed so that the background of the author(s) or originator(s) can be assessed. Education and experience in the field of knowledge or upon the topic being discussed are important factors if deciding if an information source is credible. Reliable sources include bibliographies and citations with footnotes. If new information is being relayed, sources are as transparent as possible with the research, including sample sizes or other indicators of raw scientific data. Editorial board listings in collective works should give some indication of the backgrounds of those listed.
2. Viewpoint/Agenda--Assessing the political or organizational affiliations of the author/originator can help selectors decide if the information is biased and in which ways. Selectors should be familiar with political buzzwords/dog-whistles, overtly political or ideological publishing concerns and with authors that produce so-called conservative or progressive works exclusively.
3. Timeliness/Currency--The currency of a work is important. A book written about events that are very current can lack the broader hindsight and increased context that the passage of time can give researchers. At the same time, new works written about topics that have been "left lying" for some time are often steeped in revisionism, which is frequently at least somewhat political or ideological.
4. Objectivity--Selectors need to be aware of their own biases and, when possible, err on the side of balance rather than mentoring or ensuring that what they see as the "correct" take on controversial issues or contentious points of information is the one favored in a collection.
A librarian's role in helping the community find common ground is to make certain that the sources in the library's collection are selected following guidelines similar to these. If a work is in demand but obviously biased or incorrect or factually selective, the correct approach is to endeavor insofar as possible as to include works that balance that, as directly as publishers make possible.
If the question is how do librarians ensure that misinformed people don't share incorrect information one with the other, then librarian play no role in that whatsoever other than to be ready to point those willing to do more research to quality information.
Librarians must be willing to accept the fact that some fraction of society will be misinformed or wrong and seek to misinform others. No other option exists in a free society.