For helping the mortal hero Odysseus return to Ithaca in the case of The Odyssey. Hermes warned Odysseus that the witch Circe would turn him and his men into animals and that he should eat a special herb to protect himself. He also delivered a message from Zeus to the nymph Calypso, ordering her to release Odysseus from her island.
For participating in the creation of the first woman in the case of Prometheus and Pandora. When Zeus ordered that Hephaestus create the first woman, Pandora (in order to punish Prometheus for stealing fire and giving it to mankind), each of the gods gave Pandora something. Hermes gave her the ability to lie and deceive (and seduce).