Credibiity check

It strikes me regularly that it is really hard to know how to check the credibility of a lot of things today. For example, does someone's mere appearance on a credible program or mention in a credible newspaper count for anything? I was trying to learn if someone who has written a book (so what?), been interviewed on a couple of radio shows (does that say anything?) is regarded at least positively by clearly knowledgeable people in the field. I failed to get anywhere. Published babble from unidentified people on websites is of no value in such a case.