It is coming from both ends. You have a sense of a world and what the plausibility of that world ought to be, and you explain to the players what that is, so they have their expectations set. And if you are talking strictly about, here is a realistic setting and the GM is trying to do only what would be plausible in the real world, I think it is still something where the GM has to do the mental work to figure out what is plausible, but the players are ultimately the ones judging his or her decision. So I don't think plausibility magically vanishes, it just means it doesn't exist in a vacuum. Like if you are using real world physics, as a GM you probably want to find out how real world combustion works when that sort of thing comes up. That isn't just about player expectations, because if their expectations aren't in alignment with what would happen, when they call foul, the GM can show them, 'no this is what happens if you fire a bullet through a full tank gas in the real world'.
I do think it is totally fair to reach out to players though and to not pretend like you know things you don't. For example if I have a player in my group who is a doctor, I am probably going to ask him medical questions during a scenario so I can get things right (like "how long does blood take to dry"). I think that is fair. If you have players at the table who know things, bringing in their knowledge can be useful.