There are many places that confirm this in scripture. I will give one or two. Paul said something like...one of the gifts the Holy Spirit gives to some men is the ability to know whether a message is from God or is from another Spirit. And in another place, he said he was headed for Some certain place and that he didn't exactly what would happen, but the Holy Spirit kept telling him there would be prison and beatings for him. Other places, the Holy Spirit told them to send 2 men to work for God and either told men to go to a certain place , or, conversely, prevented them from going to a place.
But I guess my main point is that there is a gift given to some men by which they can tell if a message is from God or from another spirit.
So it is not good or right to fail to take notice of this and insist that no man can ever know if another man is speaking by the Spirit.
But someone who doesn't have the gift to know can search scripture to see if a man who preaches fear of God and humility is speaking unscriptural nonsense. Now some men give Epi a very hard time because they do not like to hear that anyone who puts their hand to the plow and turns back is not fit for the kingdom of heaven. They do not like to hear that God has, and can, change His mind. They do not like to Hear that they should fear they could be cut off or disqualified. They don't even like to hear that they are in a race and must run so as to win. And because they don't want to hear these scriptural things, they say he is dangerous and should not be listened to.
But even if a man has not been given the gift to know if a message is from God, he can check the scripture to see if these things are so. He doesn't have to heed another man's warning to not listen. Scripture will show if this message is true that the safest path is to fear God, who can cut off and graft in, and to walk humbly.