One thing I in theory like about negotiations is that they've formalized motivations/pitfalls into 12 rough categories: benevolence, discovery, freedom, greed, higher authority, justice, legacy, peace, power, protection, revelry, and vengeance. These can be expressed in different ways – among the examples is a knight with Freedom as a pitfall, because he sees the world as a web of duties, and also a local ruler who also has Freedom as a pitfall because everyone needs to obey the law and pay their taxes. Mechanically they still work the same: if you try to use freedom as an argument during a negotiation, that round automatically fails and they lose 1 point of both Interest and Patience. This makes it easier to adjudicate whether an argument is particularly suitable, neutral, or bad. And of course you can take actions during or before a negotiation to try to discern a target's motivations and pitfalls.