How do you identify a real prophet from a fake one? Look at all the people who believed Mohammad for example.
There are an number of criteria by which a true prophet of God may be determined. First, we learn from the scriptures—
FOR every high priest taken from among men is ordained for men in things pertaining to God, that he may offer both gifts and sacrifices for sins: Who can have compassion on the ignorant, and on them that are out of the way; for that he himself also is compassed with infirmity. And by reason hereof he ought, as for the people, so also for himself, to offer for sins. And no man taketh this honour unto himself, but he that is called of God, as was Aaron (Heb 5:1-4).
This scripture speaks of all high priests. The prophets of God are high priests, thus no prophet may take that honor unto himself, but he must be called of God as was Aaron. How was Aaron called? He was called by the voice of the Lord to Moses—
And the LORD said unto Moses, See, I have made thee a god to Pharaoh: and Aaron thy brother shall be thy prophet. Thou shalt speak all that I command thee: and Aaron thy brother shall speak unto Pharaoh, that he send the children of Israel out of his land (Ex 7:1-2)
Since the restoration of the gospel of Jesus Christ in 1830 this is the method by which prophets have been called. God gave specific instructions to that prophet who presided over the kingdom, and under those directions new prophets have been called. These have for the most part been organized into a quorum of twelve apostles, who are sustained by the members of the Lord’s Church as prophets, seers and revelators.
But to examine any who claim to be prophets, one may apply the following tests—
1. The individual must be called by the requisite authority, as above, and sustained by the people as a prophet.
2. The individual may reveal new doctrine, but he will not declare any doctrine that would be contrary to former revelations or to the holy scriptures.
3. In answer to righteous prayer, the inquirer may receive from the Holy Spirit a confirming witness that those who represent God as prophets on the earth are indeed called of God.