The Imp's Offer is an encounter that starts at The Commoner, with the imp(not stricly adhering to the Imp presented in 3.5e Monster's Manual) Zegul telepathically communicating with one of the players. The Imp offers anything that the players desire, as long as they are willing to work for his master. Zegul is interested in the players service if it senses that the party has an evil or neutral-evil alignment.
The imp wants to fulfill the role of his master, and does not have any personal agendas. Its master, Abduxuel, is interested in acquiring power through possesion of ancient magic items. With the magic items of Adena surfacing, he is interested in expanding his network of servants, such that he can get his share of them. He knows that A'sis Quatu is selling items that can be traced back to Adena, and wants to know who A'sis is acquiring them from, and ultimately find the ancient city through his servants.
As the Zegul knows, that it appears less trustworthy than most humanoid beings, it immediately fights for the approval of the players, offering them gold and information about threatening persons(It knows who wishes the worst for the players, as it spents most of its time reading the thoughts of the people dinning in The Commoner), just for considering working for its master.