I used some empty picture frames to display my stuff, with fabric-covered cardboard to stick the pins in. It worked pretty well!
As well as selling earrings, necklaces and brooches, I made and sold hair bows. I made quite a few sets. They're actually really difficult to make, plus I kept getting fond of them. I made about 7 sets, but ended up keeping 3. They work well on bags and cardigans as well as on hair! I'm really getting into these kinds of accessories.