My kids love to trade. They keep their pins on cork boards at home. Before each trip, the three of them decide as a group which pins they are willing to trade. I usually buy a lot from ebay to stock them up. Then, they divide the traders in 3 groups so they each have their own set to trade. They try to trade at least 5 times each day. (They don't always make that goal, DS14 never does, DS11 picks up his slack) They don't really care so much about what they get; they just like the whole trading process. They wouldn't know a valuable or rare pin, but they know enough not to let a little kid trade an expensive pin with them. Two trip backs their greatest trade was for Statler (muppets) They were overjoyed and probably no one else in the whole park would want that pin! They are trying to get the whole set of The Epcot countries Mickey Icons through trading.
They have had some great experiences trading with all different kinds of employees, at resorts, bus stops, shops, custodians...everywhere and other disney guests (although trading between guests seems rare).