The art of negotiation was, in essence, reading and manipulating your opponent.
Against the demons of Greed, it was the simplest thing ever for Saint Dul'Akharat to gain significant benefits merely by showing his worth and his reluctant willingness to cooperate.
Afterall, something too easily achieved holds very little allure, and something that had to be fought and risked for would be more treasured, regardless of its true value.
At that moment, due to his highly impressive act of breaking apart the black sphere with but a single thought, the demons thought that they were in the presence of a power mightier than even their Dark Lords, and probably even at the Dark Saint level!
The power structure of the Realm of Sin was actually pretty simple.
Imps.
Lords.
Dark Lords.
Dark Saints.
Seven Sins.
The Devil.
And thus, with just shrewd negotiation skills fully taking advantage of the Dark Lord's greedy nature, Saint Dul'Akharat got himself a critical resource!