|"Scrag the brat."|
The story ran that we were stuck on a thickly populated planet with a low tech level, corresponding to present-day Earth. We could see that the Referee was trying to keep us under his thumb for a few runnings ... but I'd learned the way to get around this Ref was to think completely out of the box, especially by doing anything shocking. It tended to throw him off his even keel, so that he he would think less practically about ways to stop our plans.
We needed money. So we kidnapped an elementary school. We secured the doors, rounded up the little brats in the gymnasium and shot a few seven-year-olds to show the others we meant business. When the army arrived to surround the school and bring us our money, we killed everyone in the gym with some grenades and shot our way out.
There is no way we should have lived. But since the Ref spent most of that session with his jaw hanging open, not believing we were actually willing to scrag kids, it was easy to manipulate the session to get our money, buy a ship and get off planet.
That's what I remember most about playing that campaign ... getting around the DM. We were 17, in our last year of high school, and that seemed the most important thing. The best way to win was to steal more than the DM was offering. To force him (it was never a 'her', not then) to give more than he wanted, because it was logical.
Logic, of course, defined by the better argument.
There are things 17-year-olds don't think about, such as what the actual approach the army would have taken, or how the planet would have been shut down afterwards ... they haven't had enough experience not to get thrown by the events and to concentrate, instead, on the likely response.
I have played, naturally, with people who have tried to get around me - and once upon a time, they succeeded regularly. Now, a little less often, but still I make mistakes about giving too much treasure, too much power, or too many concessions, when I should probably kill the players instead. I think every DM who has played for a length of time can remember, with embarrassment, things they have let players get away with that should never have happened. A magic item which was far too powerful. Friends with far too much influence. A situation escaped far too easily. It happens. No matter how dearly you hold the sandbox motif, sooner or later your judgment is going to get skewed in a particular instance and you'll find yourself regretting it.
The typical DM reaction is to find ways to snatch back that item, or that monstrous pile of coins that should never have been given, typically by some trumped up circumstance which invariably leaves the players feeling bitter and cheated. I don't recommend this.
I have found from experience that there are only two practical, worthy responses:
A) Suck it up. You fucked up as a DM, they've gotten their haul and now you're just going to have to remain stoic through the next score of sessions. Don't whine, don't even admit you've made a mistake. No matter how lame the proceedings, you so best to hold your tongue and act as though this was your intent all along. Chances are, your players will be happy even if you are not, the money will run out, the item will get lost of its own accord when the player does something legitimately stupid, circumstances will change and so on. If you work harder to keep things on a tougher course in future, the players will look back fondly on those heady days when coin was plentiful and the whole incident's flaws will be forgotten - even by you, the DM. You can't fix it, you can only swallow it down and move on.
B) If the error is so HUGE, so obvious, so obtrusively destructive to your campaign, talk to the players not as a DM, but as a person. "People, I'm deeply sorry, I'm a fuck up, I should never had given all of that treasure, I should have insisted that you fight your way out, and I didn't. Please, for the sake of the campaign, I need everyone to sacrifice their gold and magic items - we'll mark it up to a dream, and in future I promise to do better."
Believe it or not, this works. If you present it very reasonably, you have the benefit of the player's knowing that yes, they've gotten something they didn't deserve, and in fact they have a feeling themselves that it is too much. They may make a joke or two at your expense, and they have a right to do so; you fucked up. I have endured many a jibe, some of which are still made years later, as in, "If I had that vorpal blade now ..." When this gets said, I remember point A and I suck it up, I grin, I make some suggestion that there's a vorpal blade somewhere, and the matter is dropped. All in all, a very reasonable arrangement for a situation I created, that I had to uncreate.
To emphasize, you achieve nothing as a DM if you try to uncreate that situation through divine intervention. Too much intervention is what created the mess in the first place. Your players tried to manipulate you with their sad, puppy dog eyes, wanting only to go up a level and feel powerful, and you fell for it. You bypassed the system for their sakes, or you built a system that was far too generous in the first place. Confess your failings, right them outside of the game format and start with a clean slate.
It's the only way, if you want players to show your world any loyalty. Talk straight with them, and they will play straight with you.