I put two sets of BD on the market, one sold after a bidding war, the other sold at original posted price.. so its most likely just bad timing : you are both on at same time wanting the same thing and probably for the same reason : a nation mission. The market goes up and down : few weeks ago it was pretty dead, currently its manic and prices reflect that somewhat crazy demand ; for why, who knows : quite lame cards are going for silly money, very useful and deadly ones cant find a buyer ; example : duplicate cards going for more than 20cr is madness : 50% fail rate.. that's 40cr to duplicate a card (and you can still bomb out even with 2 tries) ; what card is worth that? , meanwhile Call Leviathans have dropped to 12 or so and still dont sell.
It wont last, the market will settle back (barring an all out port-war kicking off) and you'll start seeing cards failing to sell and prices dropping back : just have to be patient.
As for cancelling the mission : that's plain daft : you will lose all you have done so far on it and have to repeat all that again next time : it wont go away or expire, just leave it for a while and come back to it when you have gathered the cards needed. Nation missions aint supposed to be easy, else-wise, everyone would be a duke a week after they start : just chill, it will happen and then you'll wonder what all the fuss was about.