If you have a suspicion of a cheating player, you report them in a ticket via the link Raider posted. The staff will check their accounts and take appropriate action against cheaters, and no repercussions on the reporter if they turn out to be legit. I disagree with the mentality of ignoring possible cheaters who degrade the game for everyone, it is on the entire community to purge these low-life dishonest cheaters from our game.
9 times out of 10 people with the same nickname are multi-accounts, the 1 time they are friends sharing a theme for their names won't matter, as the staff will be able to determine that easily and no action will be taken.