If this verse be true, and it is, then the deception of a mans heart is so deep into his subconscious that he rarely without the help of God would ever know if he is deceived.
You can do a search of the internet and find literally a thousand site dedicated to exposing false teaching and heresy in and among the many denominations of the Body of Christ. Yet each of these groups in and of themselves has some major flaw in their own doctrine and practice while pointing fingers at another. I am reminded of Gal 5:14, 15 For all the law is fulfilled in one word, even in this; Thou shalt love thy neighbour as thyself. But if ye bite and devour one another, take heed that ye be not consumed one of another. There is an obedience to Rom 16:17 Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them. The whole point of the dividing of the body of Christ into divisions was in and of itself carnality according to Paul. And today what has led to some of this dividing was either a lack of love on how one confronted another on their false teaching. Keep in mind it was not a one sided affair the receiving party also was unable to receive and search the scriptures and see if these thing were so. And because of the introduction of so many new versions of the Bible out there, it seems to leave each man to his conscious to decided what teachings and doctrines are false and which were not, and they had somehow left out one main ingredient in the whole mix, the Holy Ghost. The Holy Ghost would have us all in unity not division.