How can you tell if the information posted by individuals on Internet genealogy sites is valid? Some sites have sources, others don't. How do you know what, and when, to believe something you find online?
A good rule of thumb is ... Don't trust anything you find on the 'net (or elsewhere) if it doesn't have sources.
Without sources you can't verify it, and you don't know whether the information came from a reliable source or whether it came from Great Aunt Martha who may have some of it right, but may have mixed up a lot too. Or, maybe the info came from a book written by someone 100 years ago who didn't have access to sources we have now, or who just plain got it wrong.
Perhaps the information was transcribed for a web page from a book source. That book source was transcribed from a microfilm record which was itself transcribed from the original. The chance of human error is greatly increased with each succeeding transcription. Even if the information has a source, you should double-check it personally, either from the original source or from an independent source. VERIFY, VERIFY, VERIFY!
When in doubt, remember ...
Genealogy Without Sources is Mythology.