He didn't then.  You get to know more about somebody after You own their soul.

"Pilar Pineda, does your parasite still claim to have business with Me, or some other reason I should not devour it here and now?"

"It continues to claim that it's here to offer You a deal, Lord Dispater.  It says it's a super-amazing deal.  It says that part of the conversation should just be the three of us, and wants You to tell me to guarantee its privacy too."

"Oh?  And it doesn't even want Me to promise not to eat it afterwards?  Acceptable, and consider yourself told."

"Be about your business with My subordinates then, Carissa Sevar, priestess.  And you may find it amusing to know -"

"Don't tell them yet!"

"I admire courage, but not so much courage that I get interrupted while I'm talking."

"Sorry!  But Carissa Sevar is super not allowed to know yet about how you got one over on her!"

"According to who?"

"Tell you shortly!"

"Priestess, Carissa Sevar, be about your business with My subordinates while I talk to this thing and then, possibly, eat it."

....yes absolutely though she is DEEPLY CURIOUS how Dispater got one over on her. Hopefully it wasn't about anything essential.

A lesser devil will appear for them, to escort them to where Counts of Hell and some lesser contract devils of Chelish affairs have gathered to sell souls and options on souls.

"Speak, parasite."

"It's really bad for Asmodeus's interests if Carissa Sevar knows about that trick you played on her."

"And your interests."

"And the plotting Carissa Sevar's interests."

"Pretty much everybody's interests, actually!  Erastil?  Gozreh?  Calistria?  Not in their interests either!"

"And why would that be?"

"Obviously if I was going to explain that I would have already!"

"Are you under the impression that you are funny?"

"Yes."

please eat it please eat it please eat it Lord Dispater please eat it

"Whether I believe you about Asmodeus's interests or not - you have one chance to present me with a deal interesting enough that I don't just eat you."

"One +6/+6/+4 headband and one +4/+6/+6 headband, in exchange for the guaranteed death of Cayden Cailean!"

"Well now, that is an interesting deal.  Seems like something of a low price, for the death of a god."

"Cayden Cailean has already set Himself on a course that'll very likely end with His death!  That price is just for His death becoming guaranteed to happen.  I wouldn't cheat you by demanding the price for Him just like dying out of nowhere, when all I really have to sell is the guarantee!"

"I do think I'm funny, Mister Dispater.  In fact, I literally can't help it!  But that doesn't mean I wasn't honestly here to cut an honest deal with you."

"I'm not willing to just take your word for that guarantee, godling, or even your oath."

"You promise not to do anything with it or convey it to anyone or hint about it or intimate it etcetera etcetera for a period of one year, and I give you information that you could use to bring about Cayden Cailean's death after that year if He's not already dead."