FFA games are inherently unfair because they immediately violate the main principle of fair play:
"Play One-on-One." (without the help of partners, cheats, third-party programs, etc.)
As soon as 2 or 3 players form an alliance against one player, it's no longer a fair game.
Therefore, it's difficult to apply "generally accepted rules" to FFA games if they are already inherently unfair.
For example, in Civilization 5 and 6, all games are FFA, and here's a typical situation in Civ 5: a player writes to his neighbor, "I'm being attacked, lend me some money, I'll pay it back right away" (even though no one is attacking). The neighbor lends him money. The player upgrades his troops and attacks that neighbor who gave him the money and defeats him. Profit – he defeated the neighbor and no one is left to return the debt to. And after that, a fight begins.
This is a real, common example from Civ 5 to illustrate what an FFA game is like.
Therefore, Dirty is right in the first point:
1. Every FFA = A Fight