A true prophet is 100% accurate.
Deuteronomy 18:20-22 But a prophet who presumes to speak in my name anything I have not commanded him to say, or a prophet who speaks in the name of other gods, must be put to death.” ²¹ you may say to yourselves, “How can we know when a message has not been spoken by the LORD?” ²² If what a prophet proclaims in the name of the LORD does not take place or come true, that is a message the LORD has not spoken. That prophet has spoken presumptuously. Do not be afraid of him.

When a false prophet is caught he will say “OK. But I’ve repented and the LORD has restored me to the office of the prophet or ‘The Prophetic’. You have to obey me again now.”
This is why the LORD said you shall never be afraid of (listen to) him again. Yes, the LORD will forgive him if he repents. He may become a fine Bible teacher. The LORD is merciful, so that you will not be constantly fooled by false prophets, Because He will never use him in that way again.

This is for your protection. Any one who is not 100% accurate and claims to be a prophet or work in ‘the Prophetic’ is nothing more than a con-artist or a self deceived lunatic!

This is why the prophet Jonah was so upset. see Jonah 3:10-4:11. He prophesied Nineveh’s destruction but then God was merciful and relented. Since it did not come to pass right then that means the LORD would never use him again in the prophetic office. God’s response was if you lost you ministry and thousands of lives were spared wouldn’t that be worth it?

1 Timothy 6:20 Timothy, guard what has been entrusted to your care. Turn away from godless chatter and the opposing ideas of what is falsely called knowledge.

Jeremiah 23:16-40 warns of people who say “thus Says the LORD” and interpret or “prophesy something the LORD has not spoken.” They are “deluding you” and speak “out of their own minds, not from the LORD.” They “prophesy lies, and deceit of their own heart and steal my words from one another.” God says “I am against those who lead my people astray by their lies and their recklessness, when I did not send them or appoint them” (NRSV)

Ezekiel 13:1-14:9 ...to those who prophesy out of their own imagination: ³ Thus says the Lord GOD, Alas for the senseless prophets who follow their own spirit, and have seen nothing! ⁶ They have envisioned falsehood and lying divination; they say, “Says the LORD,” when the LORD has not sent them. ⁹ My hand will be against the prophets who see false visions and utter lying divinations; ¹⁹ You have profaned me among my people for handfuls of barley and for pieces of bread, putting to death persons who should not die ...who listen to lies. Because you have disheartened the righteous falsely, and you have encouraged the wicked not to turn from their wicked way and save their lives; ²³ therefore you shall no longer see false visions or practice divination; I will save my people from your hand. Then you will know that I am the LORD.
Ezekiel 14:9 If a prophet is deceived and speaks a word, I, the LORD, have deceived that prophet, and I will stretch out my hand against him, and will destroy him...10 And they shall bear their punishment—the punishment of the inquirer and the punishment of the prophet shall be the same. (NRSV)

These are the ones who sincerely think God is speaking through them, but it is really their imagination. They do more harm than good. Misusing God’s name in this way is breaking the 3rd commandment. See Exodus 20:7 Notice also that the ones seeking after those prophets will be punished just as severely as the prophets themselves.

Deuteronomy 13:1- 3,5 If a prophet, or one who foretells by dreams, appears among you and announces to you a miraculous sign or wonder, ² and if the sign or wonder of which he has spoken takes place, and he says, “Let us follow other gods” (gods you have not known) “and let us worship them,” ³ you must not listen to the words of that prophet or dreamer. The LORD your God is testing you to find out whether you love him with all your heart and with all your soul. ⁵ That prophet or dreamer must be put to death, because he preached rebellion against the LORD your God... he has tried to turn you from the way the LORD your God commanded you to follow. You must purge the evil from among you.

1 Kings 22
400 false prophets tell Ahab to go to battle and the LORD will make him victorious.
Micaiah, the true prophet, who speaks only what the LORD tells him, says in his vision The LORD allowed a lying spirit to go in to the mouths of the prophets to lead Ahab to battle so he would be killed.

1 Kings 13
God sent a prophet from Judah to rebuke Jereboam. The Word of the LORD said not to eat or drink anything in the land of Israel , just rebuke then go home to Judah and not go back. An old prophet heard of it and went to Judah and found the Young prophet and asked him to come back and fellowship, eat and drink. The young prophet told him why he could not. Then the old prophet said an angel appeared and told him to go get the young prophet and bring him back, but this was a lie. The young prophet believed the old prophet and went back with him. The LORD said because he did this he would die. On the way back home the young prophet was killed by a lion. Just because someone, even a true prophet, says “the LORD said” or “an angel told me” does not mean he is not lying or has not deceived himself. Always check: #1. What is said with the scriptures. To do this you must know its teaching by heart. #2. By what God has already told you. This is not a game. Your life depends on what you know and how you act. The prophet Hosea said we parish because of the lack of knowledge. Hosea 4:6

In Acts 16-18 We find a woman prophesying the truth, in yet Paul knew she was demonic. Its not what she said but the fruit it would have brought.

Jesus said:
Matthew 7:15-23 “Watch out for false prophets. They come to you in sheep’s clothing, but inwardly they are ferocious wolves. ¹⁶ By their fruit you will recognize them. Do people pick grapes from thornbushes, or figs from thistles? ¹⁷ Likewise every good tree bears good fruit, but a bad tree bears bad fruit. ¹⁸ A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit. ¹⁹ Every tree that does not bear good fruit is cut down and thrown into the fire. ²⁰ Thus, by their fruit you will recognize them.
²¹ “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven. ²² Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles?’ ²³ Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!’

Paul said:
2 Corinthians 11:13-15 For such men are false apostles, deceitful workmen, masquerading as apostles of Christ. ¹⁴ And no wonder, for Satan himself masquerades as an angel of light. ¹⁵ It is not surprising, then, if his servants masquerade as servants of righteousness. Their end will be what their actions deserve.
Galatians 1:8 But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be eternally condemned!

All Biblical quotations taken from the NIV unless otherwise noted.