Kartia Researcher:
The Adventure Guild is very famous, almost everyone knows about them. If they're the ones who sent you, I'm sure you're trustworthy!
To do the basic mission quest, Kartia's Labyrinth (Solo), you have to do the "Incarnation of Greed Zellaka (Solo), Incarnation of Jealousy Pelline (Solo) or Incarnation of Gluttony Kalios (Solo)" quests from Kartia Researcher.