In short, buyer beware . While not all commercial sites try to sell something, they nevertheless warrant closer scrutiny than a government site. Frequently, the cost of maintaining a site is supported through advertisers' links. Many are sponsored by educational institutions or government agencies. The URL may have a variety of endings.
Personal homepages are comparable to vanity publishing.
The document should give biographical information, including the author's position, institutional affiliation, and address. Look for an address, telephone number and email address for the author so that you can request more information on his or her work and professional background. See if the author's document is linked to another document you trust. If so, assume that the information will be presented in the best possible light. Find at least three other sources that support this source.