Everything in Hell is a game, though most are pieces rather than players. Dispater has made of Dis a form of the game that He considers civilized, a prototype organization suitable on which to run the rest of the universe after Asmodeus conquers it, or even before then for anyone sensible enough to visit Dis and imitate its regulations. Anyone who thinks Dis unimpressive, as a Hellish civilization, ought to visit literally any other layer of Hell.
Everything in Hell is a game, and when you come before Dispater with a spark of cleverness to execute an interesting trade, He is not the sort to ruin the game by demanding to see all your cards directly - though He'll happily read out more from your tiniest hesitations than mortals would imagine possible, if they didn't understand probabilistic reasoning and entanglement. Dispater will not, at any point, try to pierce past the Crown of the Most High and look into Aspexia Rugatonn's own mind, who holds the cards that the true Carissa Sevar will have kept in reserve.
But this diminished pawn sent before Him? For the price she's demanded, Dispater will permit His true self to ask three questions in return, and see what her altered mind says of them, before deciding her price. The true Carissa Sevar must expect to have her work tested, after all.