Suppose you have some pesky friend(or enemy) who wanted to mess with you and accepted some trade when you weren’t looking. Or you just misclicked. 2 times.
But I think this calls for unaccepting trades. My idea is your trade counter/accept/propose takes 30 minutes to go through, plenty of time to undo it if need be. The reason why waiting for the trade to go through is better than simply undo-ing a trade is because if your pesky friend is particularly malicious and evil, he’ll do this trade when the other person is online, not giving you any time to undo it.
I dunno if this feature would be any good, but this is just one of my thoughts.