When evaluating a source found on the web, don't just look at the source. There are sites that may look very professional and credible that are actually promoting a certain agenda or viewpoint. If you are unfamiliar with the source, it is always a good idea to open a new tab and do a web search on the source and/or the organization that is providing it. This is what is called "lateral" reading.
This short, online video from Mike Caulfield at Washington State University provides a good introduction:
There are 3 more short videos in this series, all with useful tips: