The two issues are often the same, since many GEDCOMs are exports from such a site.
And strictly speaking, a family site is a source. That's where the information comes from, it was probably family tradition contributed by a descendant, the person who put it on Wikitree was giving hearsay evidence, true, but not inventing anything. Good family sites often have sources.
My practice is to look at the changes page. If there is any evidence whatsoever that someone has been improving the profile after the initial upload, I tend to be lenient. If the profile was uploaded in the days when a "first-hand knowledge" lie was automatically generated, and not been touched since, I mark it as unsourced and if possible slap a project sticker on it to really call out the bloodhounds.