My approach is to take what I know of the situation and the game-world and apply them to my decision-making, usually with some random element thrown in so that even I'm kept guessing at the outcome.
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Now here's what I think is key: many of these setting-imposed constraints are transparent to the players and the adventurers alike.
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what we're talking about is a spectrum of transparency in the referee's decision-making. How much agency do the players and their characters have? To what degree does the setting constrain the range of likely consequences and outcomes?
I like the notion of "transparency" here.
Negotiating stakes is transparent - if a player says "I want to do X" and the GM responds, "No, that's impossible for reasons ABC - but you might get away with X* if you're prepared to take risk PQR", then there is no "gotcha". The player can make a decision knowing what the constraints are and consequences are likely to be.
A shared grasp of genre, and of the reason why we're all sitting around the table playing this game together, can also help - apart from anything else, they reduce the amount of times the GM has to say "No", and also make it easier to agree to what is at stake easily and with mutual understanding.
Shared knowledge of the parameters for permissible action in the gameworld - like the duelling rules - is obviously another way to foster this.
Conversely, in a game in which (i) the players don't know what fictional constraints are operating on their PCs, and (ii) don't know what is at stake in their various options for action resolution, and (iii) can't find out by asking the GM, and (iv) can't find out by having their PCs make reasonable ingame inquiries, is one where I would start to worry about an excess of GM force. Even if (iv)
is in place, if (iv) is compromised by a failure of (ii) - that is, the players can't be confidant in what is at stake in making inquiries (eg the GM might decide that the person to whom they talk to try to learn about what is going on tips off the inquistion) - then I would worry about an excess of GM force.
I also find transparency - in this broad sense - is a better approach to the game then invocations to "trust the GM". A transparent GM doesn't need to ask the players for trust. Either his/her game will be worth playing - as I quoted Edwards upthread, the GM will frame situations that are " are worth anyone's time" - in which case trust will be earned without being asked for, or the game will not be worth playing, in which case calls for trust will be redundant.
Conversely, calls for "trust", and reassurances that from the big pictures perspective of the GM the game is great, don't do much for me.
Of course, their might be micro-moments of trust required in a given session - the PCs are captured, and for play to proceed smoothly they need to rely on the GM to frame the escape (or ransom, or whatever) scene cleverly. And of course a GM can frame a crappy scene from time-to-time and be forgiven. Or to translate these cases into a more sandboxy-idiom - the players might find themselves struggling for a bit to get a full sense of the significance or ramifications of the choices they are making for their PCs, or a GM might accidentally "gotcha" the players because something was not revealed that ought to have been.
Still, I think there are genuinely different ways of approaching the game here, and that there are definite tehcniques that can be used to make player choices count, and to make it clear to the players that their choices count. And transparency is a key part of this.