I wouldn't expect any of the companies to double-check sources, but they might flag improbable situations, like a boy becoming a father at age 8 or a woman having a baby at 60, or giving birth to three children, all with different fathers, in the same year.
I've encountered situations where a family shows up as having multiple kids, for example, Israel, Izzy, and Isadore, with the same birth date, same spouse, same date of death. That is most likely one child, not three, and should be flagged.
JoAnne Goldberg - Menlo Park, California; GEDmatch M131535
BLOCH, SEGAL, FRIDMAN, KAMINSKY, PLOTNIK/KIN -- LIthuania
GOLDSCHMIDT, HAMMERSCHLAG,HEILBRUNN, REIS(S), EDELMUTH, ROTHSCHILD, SPEI(Y)ER -- Hesse, Germany
COHEN, KAMP, HARFF, FLECK, FRÖHLICH, HAUSMANN, DANIEL -- Rhineland, Germany