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So he spoke in prayer, and from nearby Athene came to him likening herself to Mentor in voice and appearance. Now she spoke aloud to him and addressed him in winged words: ‘Telemachos, you are to be no thoughtless man, no coward, if truly the strong force of your father is instilled in you; such a man he was for accomplishing word and action.’ (2.267-272)
Athene uses deception, but for the purpose of speaking the truth.
(Telemachos:) ‘Do not fear, nurse. This plan was not made without a god’s will. But swear to tell my beloved mother nothing about this until the eleventh day has come or the twelfth hereafter, or until she misses me herself or hears I am absent, so that she may not ruin her lovely skin with weeping.’ (2.372-376)
Telemachos’s deception extends even to his own mother.
Now Helen, who was descended of Zeus, thought of the next thing. Into the wine of which they were drinking she cast a medicine of heartsease, free of gall, to make one forget all sorrows, and whoever had drunk it down once it had been mixed in the wine bowl, for the day that he drank it would have no tear roll down his face, not if his mother died and his father died, not if men murdered a brother or a beloved son in his presence. (4.219-225)
Okay, usually when you give people drugs of forgetfulness, you're starting down a really bad path. Here, though, it seems to be okay—because Helen's acting out of kindness. Still, we really want to warn you against this.