If it is player A's turn to trade and propose offers, and he proposes an offer to player B, can player C interject an offer of his own? Or can only player A "start" offers?
In a game we were playing, two players (say A and B) were trading tiles and player C interrupted and offered to give player A the tile he wanted for free, just to prevent player B from getting a tile that would have given him a Star Performer. Is that legal?
I would say by the letter of the law, it's legal, but certainly a house rule that only the active player can initiate trades is understandable, and may help keep the game moving.
In any case, you have to be pretty desperate to give away a tile for free.