Earlier this year The Atlantic published a fascinating transcript with Chris Voss, who was at a time the FBI's international hostage negotiator. It was titled "Ask a hostage negotiator: What's the best way to get a raise?".
In this conversation, Voss shares a number of useful insights, not just limited to hostage negotiations.
One of the more interesting things that Voss discussed relates to fairness:
"We call fairness the "F-word." ... you'll find that fairness comes out on almost every single negotiation, and when it gets thrown out there, it's a word that punches people's buttons in one of the most subtle ways possible."
So it's worth keeping in mind that "fairness" will be on both parties minds, and that it's an emotive issue.
"If I'm a negotiator, I'll use it against you because I know that I can knock you back on your heels emotionally. If we're in a deal, and I want to be a cutthroat, I'm going to say, "Look, I've given you a fair offer." Now, for you to protest against that, what I've just done is accuse you of being unfair towards me. And that's why the cutthroats do it because nobody sees it. It is a stealth attack from a cutthroat negotiator."
So: used strategically, someone who is unscrupulous can set a mousetrap using the idea of "fairness". If they use this technique, they're betting on the other party being uncomfortable with suggesting that they're being - gasp! - unfair.
Voss explains that you can "take a proactive approach and... diffuse it before the missile gets launched". One way of doing this is to preface conversations by stating something to the following effect:
"I want to make sure you feel I've treated you fairly. And the minute you think I haven't, I want you to tell me."