The nature of how this game is played does not facilitate a healthy market. Almost every card is either completely worthless (Vampire), And if it isn't, then its worth keeping and leveling up. This is of course my opinion just based on my observations of playing the short time that I have. Because of the fact that "like" cards must be combined means that everyone is holding on to the cards which have been realized as useful and dumping cards which don't fill any niche. Also, unless some sort of scarcity is introduced to the already existing cards, the price of everything will always slowly drop down. Maybe once a next "series" of cards is released, the current selection of cards will become unavailable outside of the marketplace.