"For I know this, that after my departure savage wolves will come in among you, not sparing the flock." - Acts 20:29
The story is told of an inspector who worked for the counterfeit department of Scotland Yard. His job was to detect the false currency from the real. When asked if he spent a lot of time handling and examining counterfeit money, he said no. He spent so much time handling the real thing that he could immediately detect the counterfeit.
The best way to detect what is false is to know what is true. And I believe that if you have a good working knowledge of the Bible, then you will be able to detect the false rather quickly, because you are so familiar with the genuine article.
I have found that people who are into false teaching don't seem to go out into the culture and win people to their convictions, because they are so weird. Instead, they come into strong, growing churches and infiltrate their ranks, saying things like, "Hey, do you want to get into the real deep things of God? Do you want to really get into heavy-duty truth? Then come over to this little meeting we are having." They go about their deception in a clandestine, secretive way.
The apostle Paul warned about false teachers who would creep into the church: "For I know this, that after my departure savage wolves will come in among you, not sparing the flock. Also from among yourselves men will rise up, speaking perverse things, to draw away the disciples after themselves" (Acts 20:29–30).
We need to be equipped. We need to be prepared. We need to know the truth, because when we are conversant with the Word of God, we will recognize when something weird comes along. We will be aware that it does not jive with Scripture.
So be a student of the Word of God.