In this section Saul has banished all mediums and sorcerers yet then goes to one wearing a costume of some sort.
So Saul disguised himself and put on other garments and went, he and two men with him. And they came to the woman by night. And he said, “Divine for me by a spirit and bring up for me whomever I shall name to you.” The woman said to him, “Surely you know what Saul has done, how he has cut off the mediums and the necromancers from the land. Why then are you laying a trap for my life to bring about my death?” But Saul swore to her by the LORD, “As the LORD lives, no punishment shall come upon you for this thing.” Then the woman said, “Whom shall I bring up for you?” He said, “Bring up Samuel for me.”
(1 Samuel 28:8-11 ESV)
So here Saul gives an oath with the LORD’s name that she will not be harmed in any way. What did God think about sorcerers and diviners?
There shall not be found among you anyone who burns his son or his daughter as an offering, anyone who practices divination or tells fortunes or interprets omens, or a sorcerer or a charmer or a medium or a necromancer or one who inquires of the dead, for whoever does these things is an abomination to the LORD. And because of these abominations the LORD your God is driving them out before you. You shall be blameless before the LORD your God, for these nations, which you are about to dispossess, listen to fortune-tellers and to diviners. But as for you, the LORD your God has not allowed you to do this.
(Deuteronomy 18:10-14 ESV)
I also love this line, the fact that the medium at En-Dor is deceived by Saul. Many who claim to speak about the future and know all about the future are often baffled and rebuked by realities here and now.
When the woman saw Samuel, she cried out with a loud voice. And the woman said to Saul, “Why have you deceived me? You are Saul.”
(1 Samuel 28:12 ESV)