At my craft shows, I try to pick a few cards to display to catch someone's eye, either the seasonal card (thanksgiving) or a wedding card, or a Valentine theme. I'll put the bulk of cards in a nice basket clearly marked by "thank you, Holiday, Birthday, but I found the photo wire thingies work well. I have no clue what they are called, but you can find them in the dollar stores, it has a heavy base with metal "fingers" that hold the photos at the end (you wedge the card in the wire). I hope that makes sense.
For halloween craft show, I found some old wooden shutters someone was throwing out. I cleaned them up and I put a hing between the two so they can fold and be self standing. The shutters were black and I hung string across to clip the cards on with cloths pins. It really dressed up the "halloween" look and i got a lot of viewers (just a few sale) but people are looking. I think if they were stuffed in a basket, no one would thumb thru them....you need an eye catcher to strike the thought "oh, I need a card for...."
I also have a card spinner I just picked up yesterday from a gift shop going out of business.......works well. only $20 couldn't beat the price!