1. Poisonous Srimad-Bhagavatam katha

    One should not hear the statements of Srimad-Bhagavatam from professional reciters, or else they will not be effective. Quoting from Padma Purana, Sri Sanatana Gosvami has strictly forbidden us to hear about the activities of the Lord and His devotees from the mouths of non-devotees:

    putam hari-kathamrtam
    sravanam naiva kartavyam
    sarpocchistam yatha payah

    “One should not hear anything about Krsna from a non-Vaisnava. Milk touched by the lips of a serpent has poisonous effects; similarly, talks about Krsna given by a non-Vaisnava are also poisonous.” One must be a bona fide devotee, and then he can preach and impress devotional service upon his listeners.

    [From Srila Prabhupada's purport to SB 6.17.41]