I think he meant how can you tell if in the report it was really in peaceful and the person that is reporting is not lieing. This is a good question actually, since (correct me if I'm wrong) scamming is 'legal' in factions/hardcore.
Erhm he can do /server survival and if he gets teleported there then he knows he was in hardcore. If he doesn't get teleported there he is in survival.
No no that's not what I meant. Imagine this scenario: player 1 really hates player 2, so he reports him and says stuff like "he scammed me" etc etc but there's no proof. This can also happen in hardcore, player 1 hates player 2 so he takes screenshots of player 2 scamming him and lies it happened in peaceful.