My players are using Create Memories to rob everyone blind

Question

I am a novice Game Master directing my first game.

My players have recently discovered the mage in the group can cast "Create Memories". The spell reads:

Permits creation of new memories in the target, without necessarily erasing the pre-existing ones. Most of the time, unless very deeply-rooted memories are modified, the person affected will feel slightly confused, but will be convinced that his memories are real. The caster determines what information he is trying to introduce, regardless of its complexity or duration.

The spell allows for a save, but typical level-0 peasants need to roll 80+ on a d100 to beat the difficulty, so most of the time they will be affected. It however allows for an extra resist throw each time their fake memories are contradicted.

The problem is that they are now using it to get anything they see that they want. For example, they see a nice sword at a weaponsmith's? They change the memories of the owner so he remembers that they already paid, and just walk out with it.

How should I deal with it? Should I just let them take anything not heavily guarded like that, and have more important things guarded by more resistant NPCs? Or should I do something else about it?

Some background on magic in the setting and people's reactions to it might be helpful. Casting does require some gestures to be performed, so witnesses will notice it, especially since magic is feared in my setting. (People know what it is, but will call the inquisition as soon as someone does something resembling magic.) If it is a small group of people, they might hold them up while the mage changes all their memories. Any guards seeing it will become really aggressive if they see it.

Answer 1

All it takes is one or two people checking the actual money they have behind the counter after the PCs leave for things to start going wrong — the merchant will still believe that they PCs paid, but the lack of money still has to be explained, and the natural explanation is that the PCs stole back the money while the merchant wasn't looking. (This is a real theft strategy that real companies watch for.) In the eyes of a merchant, that is really bad.

The PCs will very quickly have a reputation as a gang of petty thieves robbing merchants, and shopkeepers will start reacting to their appearance in their shop as if armed thieves just walked in. This will probably not result in a merchant committing violence — more likely they'll be afraid, and try to resist or escape in some way that doesn't risk harming themselves. But the instant they can, the militia will be notified, a hue and cry will be raised, or however criminals are dealt with in the local society.

Even if the PCs avoid direct confrontations with people who believe they are thieves, they will soon have a reputation. They may have a price put on their heads — probably not much by a PC's standard of wealth as thieves aren't actually worth that much to the state, but enough to encourage hard people down on their luck to do them violence.

For cases where money exchange isn't (normally) involved, they're more likely to be able to avoid unintended consequences of their spell use giving away the deception. If they want to walk into a guarded area, planting memories in the gate guard's mind that their superior authorised the PCs' entrance won't be immediately noticed. If anything goes wrong though, the conversation between that guard and the guard captain will reveal that something untoward happened, and the guard will have even stronger memories, for the purpose of identifying the PCs, than if they'd not used Create Memories in the first place. It will take longer, but they will still be identified as enemies of the sovereign and appropriate steps will be taken.

Just remember the old saying: "There's no such thing as a free lunch." Being able to create memories in a few people is unlikely to go unnoticed when the PCs are using it all the time for everything. Such power is actually more alarming to a populace and its ruler(s) than just being actual honest thieves. Once the word gets out that someone is manipulaing people's minds, the organised response against such an alarming threat to the security of the people and nation will be way out of proportion to what the players might expect.

Answer 2

The rules of a remarkable GM are simple:

1. Allow players to do whatever they want.
2. Make them suffer for it.

A sorcerer makes a smith think the money has been paid? Excellent! Sorcerer leaves with his sword. Ten minutes later the smith and a mob of peasants chase him and claim that his bewitched gold disappeared. And this particular smith is known in all local taverns for exceptional honesty, so the peasants believe him without hesitation. Sorcerer hexes them all then? Marvelous! On the way back they meet the second mob that was late, they have a dialog, realise that the guy fiddles with minds, and next time they return with a priest, and are even more angry. Sorcerer fights them? Stupendous! Now he is known, branded a villain, and the current quest giver refuses to have any business with the party anymore.

You got the method already. Never enforce any specific behavior on the party, or following their listed alignments, or even doing the quest. Just make them suffer for not following the game. Never kill the character — not fun. Make them lose possessions, abilities, promised rewards — and all this as an obvious consequence of the player's own actions.