It is not clear why the sight of Samuel causes the woman to recognise that her client is Saul. Her client had already told her that he was looking for Samuel. Perhaps as the spirit appeared, she may have heard it call Saul by name.1 Alternatively, if the spirits normally spoke without any visual appearance, the appearance of Samuel makes her realise that her client is especially important and therefore must be Saul.2
12 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.”