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Who is the audience (researchers, professors, students, general population, professionals in a specific field) and what is the purpose? Is it trying to sell or persuade or entertain?
Is the source unbiased? Is it published on a reputable, non-biased web site, or in a peer-reviewed, scholarly journal, and not from a newspaper, blog, or wiki?
Does it cite sources? More: Is the source in-depth (more than a page or two), with an abstract, a reference list, and documented research or data?Is there supporting documentation (graphs, charts, illustrations or other supporting documentation)?
Who are the authors? Are they respected and well-known in the field? Are they easily identifiable? Have they written about other similar topics? What are their credentials? Did you Google their names or check their profiles on social media?