For this it is important to turn to the Church fathers and see what they have to say about this account in 1 Samuel 28. It is apparent that there has been much conjecture about the appearance of Samuel and it is safe to categorise all opinion into the following three categories and by which fathers they were preached!
1. Samuel was resuscitated by the woman: Justin Martyr, Origen, Zeno of Verona, Ambrose, Augustine, Sulpicius Severus, Dracontius, and Anastasius Sinaita.1
2. Either Samuel or a demon in his shape appeared at God's command: John Chrysostom, Theodoret of Cyrrhus, Pseudo-Justin, Theodore bar Koni, and Isho'dad of Merv 2
3. A demon deceived Saul and gave him a forged prophecy: Tertullian, Pseudo-Hippolytus, "Pionius", Eustathius of Antioch, Ephraem, Gregory of Nyssa, Evagrius Ponticus, Pseudo-Basil, Jerome, Philastrius, Ambrosiaster, and Pseudo-Augustine.3
Note: References supplied I, ii, iii are supplied in order for validation purposes and they have been extracted from a research article by K. A. D. Smelik in his article entitled: The Witch of Endor: I Samuel 28 in Rabbinic and Christian Exegesis Till 800 A.D. Source: Vigiliae Christianae, Vol. 33, No. 2 (Jun., 1979), pp. 160-179
1 Justin, Dialogus *** Tryphone Judaeo 105 (PG 6,721); Origen, In librum Regum homilia II (Kleine Texte 83), cf. also comm. on John 20,42 (GCS10,385); Zeno of Verona, Tractatus I,xvi,4 (PL11,376); Ambrose, comm. on Luke 1,33 (PL15,1547); Augustine, De diversis quaestionibus ad Simplicianum 11,3 (CCSL44,81-6), De cura gerenda pro mortuis XV,18 (CSEL41,651f), De octo Dulcitii quaestionibus VI (PL40, 162f), De doctrina Christiana II,xxiii,35 (CCSL32.58), cf. also his epistle 43 (CSEL 34/2,105); Sulpicius Severus, Chronicle 1,36 (CSEL 1,37); Dracontius, Carmen de Deo II,1,324ff. (PL60,797); Anastasius Sinaita, 154 Quaestiones, 39 and 112 (PG89,581ff. and 764). Perhaps this is also the view of Evodius, cf. his letter to Augustine (CSEL44, 492). 2 John Chrysostom, Comm. on Matthew VI,3 (PG 57,66), Comm. on the letter to Titus 111,2 (PG 62,678); Theodoret of Cyrrhus, Quaest. in I Reg. 28 (PG 0,590), Quaest. in IParal. introduction (PG 80,808); Pseudo-Justin, Quaestiones et Responsiones ad Orthodoxos5 2 (PG 6,1296f. - may be written by Theodoret,c f. Altaner,P atrologie, 340); Theodore bar Koni, Quaestiones( CSCO5 5,222ff.);I sho'dado f Merv,c omm. on Samuel (CSCO229,81ff.). 3 Tertullian, De Anima, 57,8f. (CCSL2,866f.) (In the spurious Carmen adversus MarcionemI II,126ff.-CCSL2,1437-however, Samuel is praised, because ,,he retained propheticr ightsa lso afterh is rest");P seudo-Hippolytus,I n Regesf ragm. (GCS 1,123), not writtenb y Hippolytus,b ut by an unknowna uthor,c f. Bardenhewer. Geschichted er altkirchlichen Literatur 11, 582 and H. Achelis, Hippolytstudien (TU16,4)122ff.; ,,Pionius", cf. n. 2; Eustathius, De Pythonissa (K1.T. 83); Ephraem, comm. on Samuel, 28 (in Opera Omnia, ed. P. Benedictus, ser. Syr. I [Rome 1737] p. 387-90) - cf. however, n. 3 - Nisibian Hymn, 42,6 (CSCO 240,38f.) and 57,15f (CSCO 240,86), Contra Julianum, (CSCO174,86f) and the abstract of a sermon (CSCO 363,63); Gregory of Nyssa, De Pythonissa (K1.T.83); Evagrius Ponticus, Cephaleia Gnostica VI,61 (Patr. Or. 28, 242f.); Pseudo-Basil, comm. on. Is. 8,19/22 (PG 30,497); Jerome, comm. on Matth. 6, 31 (PL26,46), comm. on Ez. IV,13,17f. (PL25,114), cf. however his comm. on Is. 111,7, 11 (PL2 4,106); Philastrius,D iversarumH aereseonl iber 26,1f. (CCSL9,226f.);A mbro-siaster, Quaestiones Veteri et Novi Testamenti 27 (CSEL 50,54ff.) and Pseudo-Augustine, De mirabilibus Sacrae Scripturae II,11 (PL35,2179).