You can look for the author's name and the date published posted somewhere on the site. If the name or date aren't there, then the source might not be very credible. Also, If the date published is from a very long time ago and the site is talking about a topic that has changed since then, you might not want to trust the site. Another good way is to look at the URL of the source. If the URL is a .org, .edu, or .gov URL, then it's most liely credible. If it's .com it's less credible.