a. discuss, analyze, and correct misconceptions about the topic or
b. cite multiple peer reviewed resources or
c. have written a classic treatise on the particular subject or have
published multiple times in the topical area
The introduction to Craig Bohren's Clouds in a Glass of Beer has a nice
discussion of this topic. The rest of the book is superb as well.
Note that there are many examples of errors in
a. texts (Hewitt's discussion of why clouds are white in his Conceptual
Physics 8th edition, p. 481)
b. ask a scientist forums http://www.physlink.com/Education/AskExperts/ae12.cfm