So offering a deal isn't enough? So all deals are essentially, "I'll make you an offer and if you accept it, I reserve the right to change my mind"? To all you SIM or HBD players, try doing that. Submit a trade to someone else and send WIS a ticket afterward and say, "Well, I offered the deal and someone accepted, but then I changed my mind because someone offered me a better deal. How do I undo the first one"? Tell me what happens.
Technically, according to the rules I have posted, you may be right. But I know in my heart of hearts it isn't. He's reneging just because he got a better deal. If you don't want a trade accepted, don't offer it.