Flattery, as used in the Book of Mormon, is to teach doctrines that are pleasing to the carnal mind. Another anti-Christ, Korihor, admitted, the devil…said unto me: There is no God; yea, and he taught me that which I should say. And I have taught his words; and I taught them because they were pleasing unto the carnal mind (Alma 30:53). It is flattery to tell the sinner that there is no punishment for sin. It is flattery to tell the atheist that there is no God. It is flattery to tell the servant of Satan that there is no devil. These lies are pleasing to the carnal mind because they fill the heart with rationalization and self-justification. In our day, flattery is still used, both in this doctrinal sense and in the non-doctrinal sense. The next time you are impressed with the speech of a good salesman or politician, notice how many times this is done with subtle compliments and carnal mind candy.
"Anti-Christs are usually glib of tongue and nimble of speech. They are sinister students of human behavior, knowing how to persuade and to dissuade; how to attract and create a following; and how to make their listeners feel secure and at ease in their carnality. An anti-Christ is ostensibly refined, schooled in rhetoric, and polished in homiletics. He is a peerless preacher of perversion. In Faustian fashion the anti-Christ has sold his soul to the devil: his power is not his own; he is but the pawn of him who in the end does not support his own (see Alma 30:60)." (Robert L. Millett, Book of Mormon Symposium Series, edited by PR Cheesman, MS Nyman, and CD Tate, Jr., 1988, p. 177)