what is the actual difference of yelling "go ahead" and just getting shot? How about the "Direct-brain whisper projection" in the Moves Snowballing example? It counts as going aggro but without going aggro, is "Forcing hand" the same as "You know, fuck you I'm not going to tell you shit, just fucking shoot me already you pussy!" aka not doing what the one going aggro wants. How does this works when someone is just threatening someone?
Okay, the thing is, when you go aggro on someone and hit a 10+, it's not your decision anymore, it's your victim's player's.
It's up to them to decide, by any means they deem fit, if a) their character suffer harm as established, like that, no more roll needed or b) their character does as they are told.
It's their only choices, you get no saying about that choice (other than, say, picking your biggest gun to threaten them with if you really want them to cave) and it's a player thing, not a character thing.
So yeah, you're free to say "no" every damn time someone goes aggro on you and hit 10+. But that means you're also going to suffer harm as established, just like that, every time.
That said, "to do it, do it", and "make your move, but misdirect". When the victim's player's made their choice, it's also up to them to present this choice a) in fiction and b) in a way that makes sense.
If you just want to threaten someone, not actually hurt them, but make them
believe you're going to, that's manipulating someone and the leverage is "I won't hurt you", not going aggro on them. Go aggro when you're absolutely 100% determined to inflict harm if they don't cave (or you just want to inflict harm).
What if the characters can't pay? And must they pay if you choose "make them pay" or could they just walk away? Or does that move just mean, you wont get that for free this time, can this be either Barter or exchange in a favor?
If they can't pay, they don't have what they were asking for, and feel free to escalate by following with another move, and this time, be
mean.
If they don't pay the rent, take away their stuff. If one PC don't pay the train fare, seperate them. If they don't pay for a gun but take it anyway, announce the consequences and ask : "the old guy's just behind you and his hand is close to HIS gun. If you take those gun and run with it, he's going to open fire. You do it ?" If they try to negociate, put them in a spot ("that's okay, of course we can forget the rent this time... if you kill your mother.")
Any move is good in return, provided it makes sense in the fiction. Any move will push the thing forward and keep the game moving.
Of course, the PCs can also seize the initiative and responds with a move of their own. "Fucker III is coming to get the rent? Fuck it, I wait for him by the size of the door and when he comes in, I put my gun on his fat head and whisper "how do you like lead for payment, motherfucker? Forget about the rent or I blow your brains all over." I go aggro." And that's good! That's perfect, even.
(And then you think off screen and ask yourself "wait, if III comes back to Uncle empty-handed, what's gonna happen? What would III do in that situation? Use his own barter to pay Uncle and try to get back at the PC afterward? Tell Uncle straight about it to come clean? What would
Uncle do about it?" and you're going somewhere interesting.)
Hope that helps!