Quick non-studied response:
Because we know the dead do not come back to communicate with the living, we can assume that the spirits with whom the mediums communicate are not human. What does that leave, K1? Only an evil spirit would take part in an activity which Yahowah has condemned. Now, as spiritual beings, evil spirits have seen the future, so they can accurately declare it if and only if they obtain permission from Yahowah to do so.
When someone chooses to reject the truth, they choose to receive deception. And Yahowah has given us proof that He does not have a problem letting an evil spirit dupe them even to the point of setting up their death.
2 Chronicles 18
Now Yahoshaphat had riches and honor in abundance; and he joined affinity with Ahab. After certain years he went down to Ahab to Samaria. Ahab killed sheep and cattle for him in abundance, and for the people who were with him, and moved him to go up with him to Ramoth Gilead.
Ahab king of Yisra'el said to Yahoshaphat king of Judah, "Will you go with me to Ramoth Gilead?"
He answered him, "I am as you are, and my people as your people. We will be with you in the war."
Yahoshaphat said to the king of Yisra'el, "Please inquire first for the word of Yahowah."
Then the king of Yisra'el gathered the prophets together, four hundred men, and said to them, "Shall we go to Ramoth Gilead to battle, or shall I forbear?"
They said, "Go up! For God will deliver it into the hand of the king."
But Yahoshaphat said, "Isn't there here a prophet of Yahowah besides, that we may inquire of him?"
The king of Yisra'el said to Yahoshaphat, "There is yet one man by whom we may inquire of Yahowah; but I hate him, for he never prophesies good concerning me, but always evil. He is MicaYah, the son of Imla."
Yahoshaphat said, "Don't let the king speak such things!"
Then the king of Yisra'el called an officer, and said, "Get MicaYah, the son of Imla quickly."
Now the king of Yisra'el and Yahoshaphat the king of Judah sat each on his throne, arrayed in their robes, and they were sitting in an open place at the entrance of the gate of Samaria. And all the prophets were prophesying before them.
ZedekYah the son of Chenaanah made him horns of iron, and said, "Thus says Yahowah, 'With these you shall push the Syrians, until they are consumed.'"
All the prophets prophesied so, saying, "Go up to Ramoth Gilead, and prosper: for Yahowah will deliver it into the hand of the king."
The messenger who went to call MicaYah spoke to him, saying, "Behold, the words of the prophets declare good to the king with one mouth. Please, therefore, let your word be like one of theirs, and speak good."
MicaYah said, "As Yahowah lives, what my God says, that will I speak."
When he had come to the king, the king said to him, "MicaYah, shall we go to Ramoth Gilead to battle, or shall I forbear?"
He said, "Go up, and prosper. They shall be delivered into your hand."
Note: It seems evident from Ahab's response below that MicaYah spoke in such a way as to make it obvious that he was parroting the words of the false prophets sarcastically.
The king said to him, "How many times shall I adjure you that you speak to me nothing but the truth in the name of Yahowah?"
[MicaYah] said, "I saw all Yisra'el scattered on the mountains, as sheep that have no shepherd. Yahowah said, 'These have no master. Let them return every man to his house in peace.'"
The king of Yisra'el said to Yahoshaphat, "Didn't I tell you that he would not prophesy good concerning me, but evil?"
MicaYah said, "Therefore hear the word of Yahowah: I saw Yahowah sitting on his throne, and all the army of heaven standing on his right hand and on his left. Yahowah said, 'Who shall entice Ahab king of Yisra'el, that he may go up and fall at Ramoth Gilead?'
"One spoke saying in this way, and another saying in that way. A spirit came out, stood before Yahowah, and said, 'I will entice him.'
"Yahowah said to him, 'How?'
"He said, 'I will go forth, and will be a lying spirit in the mouth of all his prophets.'
"[Yahowah] said, 'You will entice him, and will prevail also. Go forth, and do so.'
"Now therefore, behold, Yahowah has put a lying spirit in the mouth of these your prophets; and Yahowah has spoken evil concerning you."
Then ZedekYah the son of Chenaanah came near, and struck MicaYah on the cheek, and said, "Which way did the Spirit of Yahowah go from me to speak to you?"
MicaYah said, "Behold, you shall see on that day, when you shall go into an inner room to hide yourself."
The king of Yisra'el said, "Take MicaYah, and carry him back to Amon the governor of the city, and to Joash the king's son; and say, 'Thus says the king, "Put this fellow in the prison, and feed him with bread of affliction and with water of affliction, until I return in peace."'"
MicaYah said, "If you return at all in peace, Yahowah has not spoken by me."
He said, "Listen, you peoples, all of you!"
So the king of Yisra'el and Yahoshaphat the king of Judah went up to Ramoth Gilead.
The king of Yisra'el said to Yahoshaphat, "I will disguise myself, and go into the battle; but you put on your robes."
So the king of Yisra'el disguised himself; and they went into the battle.
Now the king of Syria had commanded the captains of his chariots, saying, "Fight neither with small nor great, except only with the king of Yisra'el."
It happened, when the captains of the chariots saw Yahoshaphat, that they said, "It is the king of Yisra'el!" Therefore they turned around to fight against him. But Yahoshaphat cried out, and Yahowah helped him: God moved them to depart from him.
It happened, when the captains of the chariots saw that it was not the king of Yisra'el, that they turned back from pursuing him. A certain man drew his bow at random, and struck the king of Yisra'el between the joints of the armor. Therefore he said to the driver of the chariot, "Turn your hand, and carry me out of the army; for I am severely wounded."
The battle increased that day. However the king of Yisra'el propped himself up in his chariot against the Syrians until the evening, and about the time of the going down of the sun, he died.
Mediums cannot call up the spirits of the dead, but they can channel evil spirits who gleefully masquerade as the spirits of the dead. And those who seek after them make themselves their prey.
Does this make Yahowah unjust? He authorizes the deliberate deception of someone, a deception so convincing that they might forever stray farther and farther from His Covenant and His precepts and instructions. Yet He remains reliable and just, for the deceived person chose their path freely. They do not have the right to dictate which wrong path they will be enticed to follow. They have the right to choose good or evil, life or death; all other choices belong to Yahowah. He may let them choose one way or another, but it is not their right; it is His right.
Be careful not to be taken in by miracles and prophecies that come true. If the end result is to cause you step off the right path, then you know its origin regardless of how "holy" or "godly" it seems.
Hope this helps.
Richard