The best way to expose the false is to live out what is true, authentic and pure. When a government officer is trained to identify counterfeit money, he learns by handling authentic money. That is the best way to learn what is true, authentic and pure.
But the Bible does commend us when we expose the false. Here are some indisputable teachings in God´s Word:
Revelation 2:2 commends the Church at Ephesus for exposing false apostles: "I know your works, your labor, your patience, and that you cannot bear those who are evil. And you have tested those who say they are apostles and are not, and have found them liars".
Jesus Himself was strong in His warnings against false prophets: "Beware of false prophets, who come to you in sheep’s clothing, but inwardly they are ravenous wolves" (Matthew 7:15).
The apostle Paul challenges false preachers/teachers: "As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed" (Galatians 1:9).
God speaks through the prophet Ezekiel against false shepherds/pastors: "Behold, I am against the shepherds, and I will require My flock at their hand; I will cause them to cease feeding the sheep, and the shepherds shall feed themselves no more; for I will deliver My flock from their mouths, that they may no longer be food for them" (Ezekiel 34:10).
God´s Word even warns us against false Christians: "For such are false apostles, deceitful workers, transforming themselves into apostles of Christ. And no wonder! For Satan himself transforms himself into an angel of light. Therefore it is no great thing if his ministers also transform themselves into ministers of righteousness, whose end will be according to their works" (2Corinthians 11:13-15).
And in 2Timothy 3:5: "having a form of godliness but denying its power. And from such people turn away!"