And many false prophets will arise and lead many astray.
Matthew 24:11 ESV
This one is more common than many expect. There are many false teachers that do not care about feeding the flock solid spiritual food to build them up in the faith. There are many false teachers that do not care about the authority and infallibility of the Word of God and leading all to bring glory to Him.
False teachers and prophets have an agenda (regardless whether it is known to them or not). This may be wealth, power, reputation, religious or social status, thinking that it grants guaranteed access into Heaven etc. They are so deceitful because many of them may be nice and genuinely believe that their beliefs and doctrines are correct.
We must be diligent and be like a good berean and continually test everything by the Word of God (Acts 17:11 and 1 John 4:1). We must understand that scripture interprets and validates scripture.
In addition to this: solid and regular teaching of the bible, sound doctrine, regular prayer time with the Lord and a strong relationship and walk with Him, is a fantastic way to increase and sharpen discernment along with many other things.
Furthermore, let us examine our own hearts as to why we listen to certain preachers. The below sobering scripture clearly details that many choose their false teachers because it suits their own carnal desires. These people will turn away from listening to the truth.
For the time is coming when people will not endure sound teaching, but having itching ears they will accumulate for themselves teachers to suit their own passions, and will turn away from listening to the truth and wander off into myths.
2 Timothy 4:3-4 ESV
There are many false prophets and teachers that exist here in this world. Let us be diligent in praying and studying the word of God that we do not fall prey to one.