The Bible warns many times of false teachers. Here is a good list of hot to spot them:7 Marks of a False Teacher | Challies Dot Com. I would add that false teachers will downplay, mock or reject any passages you mention about false teachers. Hat tip: Pastor Timothy.
Here are a few:
False teachers miss what is of central importance and focus instead on the small details. Jesus diagnosed this very tendency in the false teachers of his day, warning them, “Woe to you, scribes and Pharisees, hypocrites! For you tithe mint and dill and cumin, and have neglected the weightier matters of the law: justice and mercy and faithfulness. These you ought to have done, without neglecting the others” (Matt. 23:23). False teachers place great emphasis on their adherence to the smaller commands even as they ignore the greater ones. Paul warned Timothy of the one who “is puffed up with conceit and understands nothing. He has an unhealthy craving for controversy and for quarrels about words, which produce envy, dissension, slander, evil suspicions, and constant friction among people who are depraved in mind and deprived of the truth, imagining that godliness is a means of gain” (1 Tim. 6:4-5).
False teachers obscure their false doctrine behind eloquent speech and what appears to be impressive logic. Just as a prostitute paints and perfumes herself to appear more attractive and more alluring, the false teacher hides his blasphemies and dangerous doctrine behind powerful arguments and eloquent use of language. He offers to his listeners the spiritual equivalent of a poisonous pill coated in gold; though it may appear beautiful and valuable, it is still deadly.
False teachers are more concerned with winning others to their opinions than in helping and bettering them. This was another of Jesus’ diagnoses as he considered the religious rulers of his day. “Woe to you, scribes and Pharisees, hypocrites! For you travel across sea and land to make a single proselyte, and when he becomes a proselyte, you make him twice as much a child of hell as yourselves” (Matt 23:15). False teachers are ultimately not in the business of bettering lives and saving souls, but of convincing minds and winning followers.