Confirming and Cancelling Question

Hi,

I am new to deckbox and have completed a handful of trades since joining. When I get bored I send out a lot of trade propositions, and I was curious about a specification on cancelling trades.

I know that on the deckbox help page it says that trades are only locked in once shipping address is confirmed. My clarification is that I am wondering is it when both parties confirm, or only as soon as the first does? Because I throw out a lot of trades at one time for the same card, and if two people were to accept them, and both lock in their end of shipping, could I still cancel one of the trades without penalty since I have not locked in my side of shipping yet?

Thanks for the help!

AJ