When we went to WDW in Dec. DS2 (age 11) was all excited about pin trading. He only traded with CMs. He'd go up to a CM who wasn't busy and ask if he could see their lanyard. They'd say yes and if he saw something he wanted to trade he'd trade with them. He's traded with CM's who were in stores, just out and about, etc. If they had a lanyard with pins DS2 would most likely ask them unless they were busy.
We only found 2 CMs who refused to trade. Both of those people were in AK.
One was a girl who was standing outside Camp Minnie/Mickey before it opened. DS2 asked he could see her lanyard, and she said no. The other was a guy who was running register in a gift shop in AK. DS2 wanted to trade him an authentic Disney chipmunk pin. The guy wouldn't trade because he said it was too small. He looked at the pin to make sure it was authentic, said it was, but said it was too small to trade with him. We just left and DS2 forgot all about it.
Several times CMs would come right up to DS2 while in line, walking around and especially waiting for parades and ask him to trade. Some of those cast members were so friendly, and it just made DS2's day. Some CMs would tell DS2 about specific pins he had. We learned some new things while pin trading at WDW.
We're going back in October and DS2 plans to pin trade once again. We just bought some pins from a lady on eBay.