Here it is: It works like this:
You say "I sidle up to Balls, stroke my finger up and down his arm and say "y'know, I'd be real grateful if Dremmer were to run into an accident out in the waste somewhere. Real grateful."
Then I, as MC, decide if this counts as leverage on Balls. Does Balls want to fuck your character? Probably he does, unless there's a real good reason to think he doesn't. I'm making Apocalypse World feel real, but also I'm not preserving the dignity of my NPCs.
If it's leverage, we roll the dice for Seduce. If you have to make a concrete promise, maybe I'll say "Balls looks at you and he's like "For reals this time? You've jerked me around before." And you can make a concrete promise if you like. If you don't follow through on that promise, maybe you can't use the promise of sex as leverage with Balls in the future.
and it works like this:
"June, baby, how about you let me hold that key card to the armory for a bit and I'll let you hold ... something else, gnome saying?"
"Eh, you know I don't swing like that, babsy. But I know why you want in that armory. Joe's Girl done fucked up, right? I hate her too. What say you let me have that sweet, sweet sniper rifle instead? That's more my kinda gun."
If the PC promises or does it, then the NPC does as well.
When you have leverage on someone and want them to do something that the MC thinks that they ordinarily wouldn't, roll+hot. On a 10+, they ask you to promise something [concerning the leverage of course] and do it if you promise. On a 7-9, they want concrete assurances right now, if possible.