Witchcraft was alive and well in Greece.
The best and certainly the most numerous examples of Ancient Greeks using magic are the curse tablets which have been found by the hundreds. They're usually inscribed in lead.
This is a curse tablet found at Pella. It says (and I paraphrase a great deal to make it readable): I call upon upon the daimones to bind the marriage of Thetima and Dionysophon, so that Dionysophon never wed any woman but me. May I grow old with Dionysophon, and no one else. Have pity upon me dear daimones, for I am alone and abandoned. Do this for me so wretched Thetima perishes miserably and let me be happy and blessed.
Such a nice lass.
Anyone could write their own curse tablet, and many did. The tablets were usually buried, often in cemetaries, or thrown into water or wells. The idea was to get the curse as close as possible to the more chthonic of the Gods. Curse tablets when they invoked a deity usually called upon Hades (Lord of the Dead), Persephone (His Queen), and Hermes Cthonius (Messenger to the Underworld). Clearly not deities you wanted to meet socially.
You could also hire a professional for all your magic needs. Plato's Republic(!) actually mentions professional magicians, of whom Plato says in Book 2, section 364C : ...and that if a man wishes to harm an enemy, at slight cost he will be enabled to injure the just and unjust alike, since [the magicians] are masters of spells and enchantments that constrain the gods to serve their end.
Apuleius in The Golden Ass calls Thessaly the land of magic and witchcraft.
A Greek witch was called a pharmakis, from which we have pharmacist and pharmacology. Their basic job was herbs, medicines and poison. The odds are very good that a sick person might go see the local witch woman rather than an expensive doctor. The brilliant historical writer Mary Renault mentions this in The Praise Singer. She has the poet Simonides explain his great old age by saying whenever he fell ill in a strange town he avoided the doctors and asked for the local wise woman.
There was a hazy zone between between Gods and Goddesses and normal humans. In between were many demi-god half-breeds who had special attributes on account of their divine side, but who nevertheless were mortal. I don't think they count for real witchcraft but some of them are very witchy.
Circe was either a witch or a minor Goddess, depending on which version you read. Either way, she had a tendency to turn people into animals.
Medea was an outright witch and used ointments and potions to both poison and heal. She is often described as a priestess of Hekate, but I suspect it's a later association. The Goddess Hekate is worth a book, but the grossly over-simplified story is she's associated with witchcraft and the darkness, potions and poison, and is almost certainly pre-Greek.
Hekate is the only Goddess whose priestesses might automatically be considered to practice witchcraft, though even in their case it's unclear. Other priestesses had no magic power of their own. They did their work through sacrifice and prayer, asking the Gods to intercede, or in the case of the Pythoness at Delphi, acting as a conduit. There was a world of difference between a priestess and a witch.
I have a scene in one of my books in which a witch woman appears. I'd love to quote it to you, but unfortunately it would be a huge spoiler.
Thanks so much Amalia for the idea of writing this.