And if the DM can't say "no"...what is the control for the exploitive players or worse? When a player just says "oh...snicker, snicker, the temple of Good is selling healing potions half of today". Does the DM just roll over and say "Wow, cool idea...your wish is so in the game player." ?
No.
You have an adult conversation and work toward an agreement. If any participant absolutely refuses to accept anything but the one thing they desire, then that person is clearly not participating in good faith, and should be asked to change their behavior or leave.
It's
exactly the same as what you would do if you were:
- Asking your significant other where they would like to go out to eat
- Offering to invite someone over for dinner, and discussing what they would like to eat and what you're willing to cook
- Having a conversation with friends and discussing whatever topics the group finds interesting
- Getting into a serious (not heated, just sincere) debate with a colleague on a work-relevant topic
- Preparing a plan for a group assignment (e.g., you're on a team of coders drafting a plan of action for the team supervisor)
- Offering volunteer labor to a third party, where you have limits on what you can contribute but wish to contribute as much as you can
- Arranging a social gathering for coworkers, looking for an appropriate time and venue
- Etc.
Now, sometimes, there are such things as bright lines here--but if they exist, decorum and respect definitely require that you mention them first, just as you should mention if you're lactose intolerant or practice Orthodox Judaism or have a peanut allergy before you dine at a friend's house. Likewise, if you know one of your coworkers has a terrible fear of heights, it would be a very serious error to pick a venue located on a high-rise balcony or the like. In the context of a TTRPG, one common example of a bright "no" line would be sexual assault.
Outside of that sort of thing though, where there are ethical, medical, or personal reasons why someone would be genuinely unwilling to accept something, it is inherent to the very idea of mutually-respectful communication that the participants be willing to negotiate. That
emphatically does not mean that anyone must always surrender, indeed, that would be the definition of
disrespectful communication, because that means at least one person is entitled to always get their way!
No one has a veto (outside the aforementioned ethical/medical/personal/etc. exceptions.) Nobody. Not the players, not the GM,
nobody. That means
everyone is expected to be lenient and cooperative.
Everyone is expected to have give and take.
Everyone is expected to be willing to budge on some things so they can obtain other things they would like to get.
And yes, this does, in fact, actually work. I find that it works quite a bit better than many other approaches, mostly because,
unlike those other approaches, it doesn't involve secrecy and trying to
divine what others know, or trying to
hide from them things that would upset them, or trying to
pretend that something is a certain way when it is in fact not at all that way. Honest, respectful communication is, in fact, one of the most important things one can pursue in any human relationship, which includes the people you game with.
If you want "limits" on anyone--the limits
are the rules of the game. That's why making good rules is important, because they're the backbone of the experience. That's why it's actually pretty unwise to just randomly knock down or ignore the rules of Dungeon World if it strikes your fancy; those rules are
very intentional, and are extremely important for producing an enjoyable experience rather than a terrible one (assuming you
want the kind of experience it offers, of course). That's why it matters so much that the rules tell the GM that, when they answer Discern Realities questions, they must be honest. And, likewise, that's why it matters so much that the players must in fact "do it to do it," they have to actually produce the fiction that
is the doing of the thing, whatever thing it might be (attacking an opponent in melee, persevering in the face of danger, closely examining a person/place/object, etc.)