Jesus warns us to be on our guard against false prophets (those who speak on behalf of God). They are deceitful and dangerous.
Jesus gives us the right to question and to discern whether a prophet/leader is false or not. It can be difficult to do this because:
1. They can come from within the Christian community or present themselves as being associated with the community
2. They will use scriptural phrases when/how it suits them
3. Those who claim to do miracles
4. Popular message/personality (which can be encouraged by those being deceived).
There are 5 areas of behaviour the majority of false prophets share: sex life is out of control, they are greedy, love power over others, they have a large who, and they are not accountable for their own shortcomings. Study to understand the Bible and know the truth (be mindful of core doctrine versus minor disagreements). Reach those who are being mislead.