What prevents mentioning the deviant shaykhs by way of warning against them? And must every preacher be a scholar, or can they be listened to in specific matters such as encouragement and intimidation?

A seeker of knowledge should not focus his effort on criticizing preachers. Rather, he should direct his zeal towards seeking knowledge and teaching it, for whoever recognizes the truth will recognize its people. The disagreements among scholars vary, some being permissible and others not. Speaking about them should be left to the scholars who weigh matters with precision. It is not necessary for a preacher to be knowledgeable about everything; it is sufficient for him to be knowledgeable about what he intends to convey to people. There is no harm in listening to him in matters he excels at speaking about.