Matthew Poole and continuators on 1 Samuel 28:8

8 And Saul disguised himself , and put on other raiment, and he went, and two men with him, and they came to the woman by night, and he said, I pray thee divine unto me by the familiar spirit, and bring me him up whom I shall name unto thee.

Both because he was ashamed to be known, or thought guilty of this practice; and because he suspected that the Woman, had she known him, would not practice her Art before him.