Definitive proof that Nocturne negotiations are rigged
By reloading a save state in an attempt to cheat during a negotiation to save time, I accidentally discovered that the dialogue is seemingly predetermined. The answer I provided didn't affect the outcome of the negotiation.
I didn't record it, but then my Loki with Wine Party stepped in both times, and both the subsequent events ended up still being the exact same.
Also I may need to confirm at which point the dialogue is actually set (although it's most likely right after the conversation skill is used).