Or you let them try a persuasion check, because that's a normal thing for a player to attempt.
I disrespectfully disagree ...
Its normal thing for player to come up with what they would like to do ... but its also normal thing for DM to keep those things in check.
Rogue cant roll for Sleight of Hands to steal a Moon.
Commoner cant Persuate king to give him the crown and title.
Barbarian cant roll Atletic to snap grown tree in half with two fingers.
Wizard cant roll Arcana to invent spell that would instantly kill everything in the dungeon.
Those are things that simply are-not-possible ...
And its your responsibility as a DM to set bar on what is possible, and what isnt.
Succeeding doesn't make him do what they want, but it makes him look more favorably on them and maybe not arrest them for high treason or something.
If that is how you want to DM ... its your choice.
All i can say is that i would walk away from such table, bcs it smells like railroading ... and i dont like railroading.
When i roll for something, its bcs i want that thing to happen ...
When you dont want that thing to happen, simply dont let me roll ... by allowing roll, you allowed the thing to happen ... that is whole purpose of that roll.
I mean ... w/e really ... do it this way, if you want to, you will learn in time ...
Just do a favor to yourself, and each time you give your players this "different" outcome ... ask them after the session end, how they felt about it ... and if they wouldnt rather preffer you to simply tell them that is not possible and move on.
You may be surprised.
