I'm a new DM for four people who are all friends (I am also friends with all of them). During the game, I observed one player turn a D20 from a lower number to a higher number a couple times with her thumb when all the players were rolling simultaneously. Both times, she verbally told me she rolled the lower number, but I also think she saw me observe her change the roll. At the time I chose to let it go, with a resolve to watch her more closely in the future.
However, another player approached me a couple days after the game, to tell me that this player was changing her rolls, and that they feel it is unfair that this player is manipulating their rolls. I'm not entirely certain that this second player didn't just observe the times I saw however.
I don't want to accuse someone of cheating if they were not, but I also don't want cheating to continue if it is in fact occurring. What is a good approach to dealing with this situation? Should I talk to the player in question, or make sure only one person rolls the dice at a time, or some other approach?
Additional information that answers questions that have come up in comments:
- We were not using any form of dice tray or dice tower.
- Each player has their own unique colored dice.
- I am not assuming that this player is cheating, however it is possible the second player who brought it up to me could be assuming so.