This is particularly crucial when adopting an evidence-based approach. You should also be critical of your search strategy and the resource you are using. Don't be afraid to amend your strategy and search a second, third, fourth time. Universities and research institutions provide information about their teaching and research programs. Specialised service centres give access to research databases.
Commercial organisations provide customer support and advertising information.
Professional bodies provide information for their members. Medical charities and support groups make their information available. Individuals publish details of their work and interests. Remember that looking at the origin of an information resource can be a guide to its reliability. Unfortunately many of these services also find irrelevant and trivial documents.