[Sombre]

Nah, commander trading isn't an exploit. Of course if the game is no diplo then it's against the rules.

I think sickle farming is probably an exploit, but it doesn't seem very degenerate. It could be that someone is able to do something really ridiculous with it, but no-one has so far to my knowledge.

Giving your commanders to another player (rather than trading) is also not an exploit, but could well be a total douche move if you're doing it to throw the game, or because of something someone did outside the game.