No, seriously, we're asking. Or rather, capitan_estaban is asking in the Multiplayer forum of the Wizards Community. He provides a few examples of situations where problems can occur, such as "Lifelink? You didn't do any damage."
From there, people talk about the official rules and their groups' usual workarounds. Among the solutions proposed are "concede only at the end of your own cleanup step," "don't allow concessions," and a variety of others.