Characteristics to question when looking for credible websites:
WHO: established expert/scholar in the field, established, reputable organization or society.
WHAT: well-written content with veriable sources.
WHERE: beware of .com because usually they are trying to sell you something (.com is short for commercial); .org tradiationally means non-profit organization, but sadly, .org domain can be purchased by a less reputable person/group; .gov means it is a government website, should be impartial representation of facts.
WHEN: the date it was published on the web or last updated. If it is old (you determine what is old age for your topic) or there is no date, you may take caution.
WHY/HOW: what is the purpose of the website? why are they sharing this information? Check out the About Us or Contact Us page to learn more about their purpose.
An ideal website has positive, good answers to all the above questionable conditions. When you start having unknowns or less favorable answers, the reliability of the website goes down.