It is always tough to use subjective judgment. Especially when trying to establish the credibility of an author you don’t know. Here are some treatments of author authority and a quantitative means to evaluate them.
http://mason.gmu.edu/~montecin/web-eval-sites.htm
Vetting secondary source authors and
how the journal of history and computing do it.
So this should give you a guide of where to start in quantitatively assigning authoritative rank.
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