Credible experts are usually affiliated with a reputable organization such as a university, professional organization or research institute, or government entity, etc. This is why it’s good to look at the author info in the articles you retrieve. Credible experts have authored works that have been characterized or identified as authoritative in the field in question (by multiple reputable sources), they have been characterized or identified as an authority in their field by multiple reputable sources, and/or by virtue of their position, they could be considered an authority (for example, an expert in a government agency).