One way that false prophets were identified in Old Testament times was by waiting to see if what they said came to pass1. However, it wasn’t the only way, probably since this would have some very practical limitations as in the case of Jeremiah and Hananiah3. Someone couldn’t wait two or seventy years to see who was speaking the truth!
This “time delay” problem is further compounded by the fact that God could be testing you6. In this, a “prophet” may perform great signs but speak things contrary to God’s word. And it’s in this, along with other examples2,3, that we see a more fundamental rule emerge. We see the prophet’s message being measured against past messages from other proven, true prophets2 – that is, prophets speaking God’s word6. Testing the things prophesied was true in the early church as well5,7. In other words, the consistency of message is paramount (and why wouldn’t it be since God doesn’t change).
Note: A ‘tip-off’ for the hearer that a “prophet of God” was actually a false prophet was someone that is always preaching peace3 (“everything’s going to be okay”). The much more common message of God’s true prophets was one of judgement, condemnation for disobedience and a call to repent. True spokesmen for God are speaking His words/message4.