I just tried a bit, what an incredibly terrible system. There's plenty of "buy" order for almost every card, but instead of just going to my inventory and click "sell at whatever price is highest now" I have to guess the price people are willing to buy it in a screen with no information about the current buy order. To find the buy order I need to open another window, go to community market place, find the game, find the card in the list, lookup what the highest buy order is and finally enter that amount. All that for maybe 5 cents.
I remember playing trough portal with dev commentary on and valve dev were absolutely obsessed with getting every little details right and making things as seamless as possible. Where was that attitude when it came time to design the steam store? If Valve gets a cut of every transaction between user, why aren't they trying to make this as easy as possible?