Simple Abstract Scam Mechanic Idea

One of the players in the Fortress Eibon games in an incorrigible rogue; he has played a succession of amoral through to sociopathic, lying, cheating, stealing murder-hobos.

Now I consider this a good thing; it's good to have players/characters that give aspects of the game a good thrashing. And it helps keep a DM on their toes.

This has had an interesting effect on my game. Originally I had envisioned the urban/home base aspect of the Fortress Eibon games, the outskirts of Yam City, to be the equivalent of the text menu interface of the old Wizardry computer RPG game: make new character; buy gear; sell gems; get unstoned; and the like.

Being a ham, I couldn't resist giving it atmosphere and character, but the explicit idea was that adventure took place in the dungeon.

However with the continued antics of the characters of the aforementioned players, and my desire to provide full agency to the players, hijinks have definitely ensued.

This has had me musing on quick resolution for such antics; I usually use d6 or a 2d6 reaction roll to adjudicate how they play out. I break down the probably outcomes and compare them to the roll result to see which way things play out.

Usually you could break down the outcomes of risky endeavors into four abstract outcomes: success; success with repercussions; failure; failure with repercussions.

For the determination of scam/heist activities, the DM makes a judgement on an adjustment, usually using a ability score modifier with further adjustment for the quality of player plans and preparations, and adjusts the results of a d12 roll by this integer, comparing the results to the table below, with the caveat that any roll that is a natural 1 is an automatic failure with repercussions.

10-12 - Success
9 - Failed Attempt *
8 - Success with repercussions
7 - Failed Attempt *
6 - Success with repercussions
5 - Failed Attempt *
4  - Success with repercussions
1-3 - Failure with repercussions

* on a result of Failed Attempt, the players may press their luck and continue their endeavor, making another roll as above but with a cumulative -1 modifier for each result of Failed Attempt *.

Repercussions are determined from what would be appropriate by the DM, with a further d6 roll used to determine the severity of the repercussions.


Example
Bill Snakehat is pretending to be a long lost distant relative of a wealthy family in order to claim an inheritance. The DM determines that: Bill Snakehat has a +1 charisma modifier; he has the signet ring of a long lost distant relative (+1); but his plan is preposterous (-3), for a net modifier of -1.

Bill Snakehat's player rolls a d12 and gets a modified result of 5: Failed Attempt. The family does not believe Bill Snakehat's claim. Bill's player attempts to press his luck and arranges for a crooked lawyer to produce fraudulent documentation to support his claim.

The DM makes the roll and gets a result of 7: Success with Repercussions. They than roll a d6 and gets a result of 6: The most severe of repercussions. Bill Snakehat receives the inheritance but a family member hires a gang of assassins to kill him.