Lineage Of Suspect
We operate under the presumption that all families are of acceptable lineage and it is permitted to marry their descendants as an initial and preferred option. Nevertheless, if you see two families continuously quarrelling with each other, you see one family that is always involved with strife and controversy, or you see a person who frequently quarrels with people at large and is very insolent, we suspect their lineage. It is fitting to distance oneself from such people for these are disqualifying characteristics.
(Mishneh Torah, Issurei Bi'ah 19:17)