I noticed that the player market just shows the lowest price. Which is completely fine because obviously everyone wants to buy the cheapest.
However, I think some tools can be added that'll make it better for players in general.
For example, how about a historical graph for said card that a player is interested in?
Historical price, average price, price of the card sold in the past week/month/year? Quantity of a particular card sold in a certain timeframe?
All these information would be very helpful especially to new players who aren't familiar with the value of cards. A player who got a really bad deal because of his/her "newbieness" could very well end up a player lost forever. I know I would be pretty disgusted if I were to be "tricked" in such a way. One would say it's a free market and caveat emptor, but a game trying to grow would be better served with a less predatory system.