Currently if a trade is opened between two players and an item is placed, then the trade is cancelled, both players will receive a message that the trade has been cancelled. If a trade is opened and only currency is placed in the window, and then the trade is cancelled, there is no message that the trade has been cancelled. If the player receiving the currency had clicked "Trade", there's no indication for them to tell from that point if the other player hit Trade as well, or cancelled the trade. The only way to tell is if they had known exactly how much currency they had before the trade, and can confirm that the currency from the trade is now added to that number. This is a big issue for GDKP raids because the raid leaders have to be very careful when accepting currency trades. If they don't check their platinum before every trade, or make sure that they are the second person to hit the trade button, then it's possible for players to take advantage of the lack of cancellation message.
One of those small things that is really annoying in the moment but something I always forget about complaining about.
