My argument is that it specifically states in the market FAQ:http://deckbox.org/help/market_faq
Do I have to sell the cards at the price I set even if the market price became lower overnight?
You have to sell at the price you had listed when the buyer pays for the order.
After I receive an order, can I discuss and negotiate with the buyer, same as with trades?
No, there is no "accept" stage for you as a seller. If a buyer sees what you have to sell and pays, you sold it. If you are away for a period of time, or otherwise unable to look at your prices and ship your received orders, please set your Vacation Mode to ON. That will prevent users from proposing trades or buying cards from you.
With this in mind, he canceled my order and relisted it immediately for higher.
What do I want out of this? The support of deckbox backing me up. If they'll allow this guy, who has removed his account anyways (because even he knew he was wrong), the moral highground, they'll do it whenever this happens to me (or you) again, and so I'll just take my buying to somewhere that will side me with me on this issue.
Yes, he did refund me. That's nice, and it's why I'll let this go between me and him. Should he be allowed to continue 'conditionally' selling cards (condition being that nissa or whatever card) doesn't jump 20$ in price over night after they sell it? I, and the FAQ think not. Possibly the FAQ and me are wrong then.