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 what you read 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.
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 webpage 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!!!
You also want to think about the source itself. Is the source a good one? After all, if Great Aunt Martha gives me information on the birth or baptism of my 3rd great-grandpa and I put it on the 'net, and source it as "Remembrances of Great Aunt Martha", that's not necessarily a reliable or accurate source. After all, Great Aunt Martha did have that fall from a horse when she was a child and she IS 97 years old......
However if I source the birth or baptismal dates with full details on the church where I saw the original record, or the published transcript of those church records, that's much more reliable.
When in doubt, remember.... .
"Genealogy without sources is mythology"
© Lorine McGinnis Schulze