Cheating is a serious problem with some groups. My baseline is always to assume a group opposes cheating, but to also give everyone the benefit of the doubt.
One of the reasons its a problem is "spotlight" time. everyone has good days and bad days with die luck. On your good days, you get to resist the powerful spell, make the difficult skill check, then kill the major bad guy with an amazing critical.
On the bad days, you're taken out of the fight with a failed save on the first round.
These balance out, over time. Everyone suffers the lows and gets to enjoy the highs. Someone who cheats gets too many highs, and is thus stealing the spotlight of attention from other players. He's taking more than his fair share of fun.
Sometimes, someone appears to have an amazing run of good luck. When that's the case, it's not unreasonable (in my opinion) to ask him to make sure he uses a big, well-marked, obvious die that everyone can see when rolling. Explain this is not to prevent cheating, but to make sure everyone knows, up front, that future good rolls are just expanded luck. Even if the guy wasn't cheating, this will prevent possible resentment later on. If he was cheating, and this stops it, the problem is still solved. In any case, in my experience if this is handled diplomatically and without accusation, it goes pretty well.
If you know for sure someone is cheating, make sure to tell them it's unacceptable. Then, go to the rolling the big die. And once you institute this rule, it's a good idea to make sure everyone (with the exception og the GM, who needs to keep information secret) is required to roll well-marked and visible dice, to prevent other resentment.
If a player seems to just be cheating to prevent a character from being killed, you might consider institutiong drama points or action dice or some other limited script-immunity mechanism that everyone can use. One reroll per game, even. Then, well-marked dice and no more player fudging tolerated.
If someone still cheats, give one warning, and explain future cheating will result in being disinvited from playing. Stck to that warning.
Spotlight time and player resentment can be serious issues, and often players don't feel it's their job to complain about such problems, leaving it to the GM to regulate them. After gaming for 23 years, I just this week had for the very first time a gamer tell me he didn't want to game with me anymore. My only recourse was to ask him to leave the game, or leave myself. As he ran one game on that night, and is roommate to two of the four other players for the other game, there was no realistic way to ask him to leave. As no one else in the group suggested I stay, I left.
The reason he gave for not wanting to game with me was that my valid, legal, toned-down from their maximum possible effectiveness characters were too powerful. As a GM, he felt he couldn't challenge my PC. As a player, my higher level of effectiveness and success made the game less fun for him. Though no one supported his claims or agreed they didn't want to play with me, two other players did say my characters were "a bit much."
Now, I would have thought that two years of gaming as a group was plenty of time to mention such problems before they rose to the "don't want to play with you" level, but apparently no one wanted to say anything. This case may have been badly handled, but the basic problem remained. Players can get very frustrated if they feel they're not getting their share of heroic action, and cheaters unfairly grab more of it.
Take steps now, to prevent a slow boil of jealousy and resentment.
Play Well!
Owen K.C. Stephens
