Use Discernment.

     But false prophets also arose among the people, just as there will also be false teachers among you, who will secretly introduce destructive heresies, even denying the Master who bought them, bringing swift destruction upon themselves.
     Many will follow their sensuality, and because of them the way of truth will be maligned;
     and in their greed they will exploit you with false words; their judgment from long ago is not idle, and their destruction is not asleep.
                                             2 Peter 2:1-3 NASB

     This is a call for the body of Christ to exercise our God given discernment (1 Cor 12:10). Understand that false teachers are everywhere. The bible warns us that they will come from within (Acts 20:29-30). This is what makes it hard. Many people are easily carried into error, because they assumed that they could trust someone that they thought they knew.
     False teachers can quote scripture and teach solid truths, giving people a false sense that they can be trusted, Then they slip in a half truth, or a stretched truth, or even an outright falsehood, but unsuspecting individuals swallow it down.
     Look at what Peter tells us about them. They will exploit you with false words, because they are greedy (2 Peter 2:3). They will tell you what you want to hear, they will appeal to your flesh, they will take advantage of you, for their own selfish desires.
     John tells us that the spirit of anti-Christ is coming, and is even now in the world. In other words, false teachers are here, with all of their false teachings designed to benefit them, and lead you away from Christ. He also encourages us with the truth that we can overcome them because "Greater is He who is in you, then he who is in the world" (1 John 4:3-4).
     We do not have to be blind to heresy. We do not have to be led astray by a false teacher. We do not have to be taken advantage of. Use the God given discernment that is available to the body of Christ. Test all things by the standard of God's revealed word, and reject all that is false (Acts 17:11; 1 Thess 5:21-22).