Newspaper reporters customarily verify leads with a second source. You should do likewise. Authority can be established by a degree in the discipline, a record of teaching or research in the field, a job in a related area, or significant related experience. They may also include a link to their home page, where you can examine their professional resume. This may take you to author's entry site.
Commercial sites exist, of course, in order to sell a product or a service.
Material from any group's site may be useful, so long as you analyze the group's purposes and possible biases. Bias Examination of the subject, author, and purpose will lead to uncovering the particular biases of the web site. In spite of claims of academic objectivity, it is, in fact, impossible for authors, reseachers, or sponsoring organizations to avoid some kind of bias. At best, the author will attempt to be fair, either by admitting to his or her biases or by acknowledging other possible positions, interpretations, or conclusions. Since the web is relatively new, almost all web pages have been written within the last five years.