Oh man, I feel for you. That totally sucks.

Yeah, in the market, there are the cooldown days remaining for certain cards. It's if they'Ve been used in battle and then put on the market, the cooldown is always a max of 7 days. I always ensure to purchase cards that don't have any cooldowns. While I've put cards with cooldowns on the market, I try to wait for them to cool down before putting them up, so that they sell faster.

Michievous Mermaid is a good one to have. Mine's only lvl 1, but she sure does come in handy a lot of the time.