Everyone knows that common fey exist, and are near manifest zones tied to Thelanis.
People tell fey stories, and also know that they have a basis in truth.
When they tell a story of the Forest Queen or the Lady in Shadow, they know they exist somewhere, even if they never expect to meet them in person
Specific knowledge of the Fey might be more common in locations near to Thelanis manifest zones, or where there a traditions of making bargains with them.
Those from Aundair know more about the Fey than most other people of the Five Nations.
Most people cant tell what a Fey is, so its not uncommon for Cultists making deals with other malevolent forces to think they are making a Fey deal.