Bias originates with the author, sponsor, or publisher. Researchers can discern bias by carefully examining both content and context. This is as true of popular magazine articles and websites as it is of scholarly monographs and journal articles. Ideally, editorial and peer review reduce but cannot fully eliminate bias in scholarly publications. Academic sources nearly always present multiple perspectives. While a one-sided source is not necessarily "bad," find others that represent a different perspective or solution to the same problem. Many topics worth researching remain unsettled. For other topics (e.g., climate change), scholars have reached broad consensus but work to refine their understanding by investigating topics/questions for which the data remain poor.
Be aware of potential bias throughout the research process. Look for indications of cultural, political, racial, socio-economic, monetary, or other biases. Remember that bias exists even within the writing of scholars and well-respected generalists (e.g., a New York Times reporter), all of whom are invested in their work. More fundamentally, researchers' writing is informed by personal experience and grounded in historical and contemporary institutions of power. Many organizations publish online content in a concerted effort to sway readers to a particular point of view. There is nothing wrong with issue advocacy, but it must be acknowledged and recognized. Again, are there other perspectives or points of view? Remember too: Omission or shading can be as damning as an outright lie.
Perhaps the most important way to control for bias is to corroborate the information you have found on the open web against other websites, or better yet against the credible information available from our library's books and databases.