Added 25 minutes later
I have a suggestion.
Whoever is caught cheating receives a reduced chance of triggering a Night Detective (ND) for the entire next game (not the next game that will be held, but the next game they sign up for!). In the case of indirect cheating (Dag), let's say it's 50%, and in the case of direct cheating (Orton), it's 25%.
And the cheater has two options. Either they get offended with the entire forum and stop playing altogether, or they honestly serve their punishment throughout the entire next game and rejoin the ranks of normal, honest players.
I don't think anyone would enjoy sitting through all the Mafia games with almost no chance of being the Night Detective.