Consider the following:
You can limit your search results in Google to pages from a specific domain by adding site:.(domain name) to the end of your search.
Example: diabetes and exercise site:.gov would find information on exercise on diabetes published only by government agencies.
The domain of a website can tell you a lot about the purpose of the site.
.com = commercial site
.net =network provider
.edu =education - school or university
.mil = military website
.gov = government website
.com, .net, and .org sites are less regulated, meaning anyone can register for a website with that domain.
.edu, .mil, and .gov sites are more regulated, and tend to be more reliable.