In my experience, it is pretty rare to find genealogical information on the internet with any source citations at all. But on one site (which shall remain nameless), I actually found a source listed!
Wilfred ***, firsthand knowledge. ... Entered by Wilfred ***, Jun 21, 2012
Considering the page is about someone who lived in the mid 18th century, it seems unlikely Wilfred has actual “firsthand knowledge”; not unless he’s immortal or has invented a time machine!