it is interesting to note that there was a lack of Patristic consensus on whether the Witch of Endor actually called up the ghost of Saul, or a demon, or if she was a fraud.
I looked at it in depth and concluded that the Bible writer presents it as actually Samuel's Ghost, for a number of reasons. One is that 1 Samuel 28 says, "When the woman saw Samuel, she cried out loudly".
The plain reading is that the ghost was actually Samuel. To read it otherwise, one would need a metaphorical interpretation of Samuel. The story repeatedly presents the being this way, eg.:
Then Saul realized it was Samuel, and he bowed his face toward the ground and kneeled down. 15 Samuel said to Saul, “Why have you disturbed me by bringing me up?”
One could see the reference to seeing a god as an implication that it was actually a demon/angel. But in THE RELIGION OF THE APOSTLES, Fr. Stephen suggests that when the story talks about the woman seeing a god/"divine being", it is referring to theosis, and how Jesus says that the deceased become like angels.
A second reason that it could be real was that the being's prediction came true, as Saul's life ended in tragedy.
Third, when it says that Saul realized that it was Samuel, it reemphasizes the point, saying that at least Saul believed that it was Samuel, although conceivably Saul could have been fooled.
A fourth reason was that the being rebuked Saul when, based on the context of God abandoning him and Saul disobeying God, it would be fitting to rebuke Saul.
I guess that there is room for ambiguity in the story on this issue, because we are dealing with another paradigm than the normal material world.