The question is about false preachers - not prophets. Who are preachers? Are they not anyone who explains or teaches about God?
We could put the 'church fathers' (CF) in this category - them and their writings which have become the creeds largely accepted by Christendom the world over for many centuries.
How do we know if they represent God at all?
Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world 1 John 4:1
Now the Bereans were more noble-minded than the Thessalonians, for they received the message with great eagerness and examined the Scriptures every day to see if these teachings were true. Acts 17:11
the NIV puts it, "to see if what Paul said was true."
How did they test the teachings of Paul? By comparing to the scriptures. When we compare the CF to the scriptures we find divergent beliefs and doctrines being espoused, taught and eventually made the new 'law'. Things which have no foundation in any verse, let alone the whole bible that offers a consistent narrative about one God the Father and His human son Jesus and their presence with us in spirit.
We know here are different spirits at work in this world - God and His spirit for good and the devil and his spirit and power in the world in this age for evil.
Now we have not received the spirit of the world, but the Spirit from God 2 Cor 2:12
you used to walk ... conformed to the ways of this world and of the ruler of the power of the air, the spirit who is now at work in the sons of disobedience.
Clearly, any may be directed to follow either spirit. Unless God expressly acts to draw a new believer into His realm, they will remain in the realm of the world and under the governance of the devil. (until such time as they are made fully aware of Jesus and the kingdom he presides over)
So any one who teaches about God may also be subject to the 'world' and not even know it. If we compare to the word - the truth once delivered, we will soon see if they speak truth or not! (This comparison is of course based on the premise that any errors introduced into the text are made apparent and accounted for)
We examine the word to see if what is taught is true. Only God can lead this endeavour. The Apostles taught consistently that there is one God - He is the Father. They taught of the human Jesus who is the Christ. They did not teach of the person of the Holy Spirit (this is answered elsewhere)
They certainly did not insist that this doctrine of a trinity - a 3in1 God become the mandatory doctrine necessary for salvation!
To even the untrained mind, this presents a mystery worth pursuing to see if the CF speak the truth or are false teachers as we have been warned about already.
You have heard that the Antichrist is coming, and already many such antichrists have appeared. 1 John 2:18
For many will come in My name, claiming, 'I am the Christ,' and will deceive many. Matt 24:5
The Spirit clearly says that in later times some will abandon the faith and follow deceiving spirits 1 Tim 4:1
We must compare to the word of God, His son's words, His appointed Apostle's words. If a teaching in contrary to these - we are required, warned, to examine and decide for ourselves.
There is a slightly humorous yet important incident described in Acts 19, an imposter was made known, and subsequently, they began burning books of things not of the word of God - a lot of them!
some of the Jewish exorcists, who went from place to place, attempted to use the name of the Lord Jesus over those who had the evil spirits, saying, “I order you in the name of Jesus whom Paul preaches!” Now there were seven sons of Sceva, a Jewish chief priest, doing this. But the evil spirit responded and said to them, “I recognize Jesus, and I know of Paul, but who are you?” And the man in whom was the evil spirit, pounced on them and subdued all of them and overpowered them, so that they fled out of that house naked and wounded. This became known to all who lived in Ephesus, both Jews and Greeks; and fear fell upon them all and the name of the Lord Jesus was being magnified. Also many of those who had believed kept coming, confessing and disclosing their practices. And many of those who practised magic brought their books together and began burning them in the sight of everyone; and they added up the prices of the books and found it to be fifty thousand pieces of silver. So the word of the Lord was growing and prevailing mightily.