Mafia

[Divisor]

Ok, everything is fine, at least until this:

*I tell both of you to check me, and tell me my role in the next day round. First one to post my real identity is the real sheriff (or the real sheriff is stupid and will die first).

Let's assume you are a citizen and mark you with "Citizen 1". The real Sheriff is "Sheriff 1" and a Mafia posting as a Sheriff is marked as "Sheriff 2".

Sheriff 2 definitely knows Citizen 1's identity, since mafias know other mafia. So he'll say you're innocent. Then Sheriff 1 checks you, sees that you're innocent and posts this after Sheriff 2.
Ergo: If citizens go by your plan and lynch Sheriff 1, it would be a mistake.

It could easily happen since we can't be here 24/7, so the fake Sheriff could post before the real Sheriff.