I see different types of dialogs between characters at the table.
Most are “sparring” : the exchange is a pretense, with ample room for expressing characters, some (little) wiggle room to find out a dramatic (as in narrative) way, but mostly the end doesn’t stem from the dialog itself. Either one side yields (GM, losing side) or not much changes. Of course, increasing the dramatic necessity (drama) of the dialog increases the need and motivation to find out. I think it doesn’t increase the odds of finding out.
These dialogs have an “expressive” function.
A different type of dialogs is when there is hidden information. I don’t mean when the stakes are informations. I mean when each side has some kind of structure and can guess and hit or miss in the negotiation. This structure can be given by “Myth” (module, past play), “Oracle” (like a motivation the GM rolled for an NPC, or a hidden vice), or some other form (like the prisoner mini game I did in Paws). Only then dialog has “teeth” and is used for “gaming”.
This second type has various forms, whether there is a GM or not being an important distinction. It can be argued that the wiggle room in a mostly expressive dialog is about finding the structure from past play. Or that information assymetry can be faked (“no meta gaming”). My point is that committing to a structure for each side makes the dialog “gamable” while making it during the dialog is something of a different nature. I am probably chasing “Quantic ogres” but in a very specific place : dialogs, because I believe it’s an important part of the hobby.
I am just making categories here. I didn’t look into the medium (direct speech vs narration) or the length of the “injection hose” (“rolling” before the dialog, midway or at the very end), or mechanics that enable players to shape dialogs (like duel of wits). But there are probable links here. I expect gamification to terse indirect speech for instance (I talk of his daughter), while expression would go with prolonged language-acts (provoking, saluting, reassuring, etc.)
The terms I chose are maybe counter intuitive, feel free to alter them. Mechanizing social skills make the dialogs un-gamable : all the juice is in the rolls, the words after that are left with a toothless expression.
Has something already been written on dialogs that can interact with the categories I describe ? By “interact” I mean, while not being necessarily of the same general scale, will not be a self contained guide on “how to play NPCs”.