Mm, reminds me of the black market ideas that have circulated and been shot down.
Basically, no. I want the only way to gain cards to be actually playing the game. Since we have a Bazaar, a market would only add to the server load and coding work, and I can't see any value in it either.
If we allow players to set prices on cards, a lot of beginners are going to be scammed, and an economy will develop around this. That's the worst thing that could happen, as it reduces the game to something really cheap and fake.