There is a full field of knowledge called E'lm Al-Rijaal which deals with every narrator and searching and assessing his authenticity. Deviat persons are known by our scholars of E'lm Al-Rijaal and their narrations are never accepted.
Famous Shia books on E'lm Al-Rijaal are like Kitab Al-Rijaal by Al-Najaashi (450 Hijri),
Rijaal Al-Kashshi (350 Hijri) ,
and Al-Fahrist by Al-Shaikh Al-Tousi (460 Hijri) ,
Ma'aalim Al-Ulama' by Ibn Sharashoob 588 hijri.
Khulasat Al Awwal by Al-Allama Al-Hilli 726 hujri.
Tanqeeh Al-Maqaal by Al-Mamaqani 1351 hujri.
and Mu'jam Rijaal Al-Hadeeth by Al-Khoei 1413 hijri.
We only accept narrations from authentic narrators who were always in the right path.