I started my 2 nieces on pin trading in Oct. They loved it so much, they only traded with the CM's
When DH and I went back in Dec we asked the girls if they wanted more pins, of course they said yes. The older one wanted Tink only and the younger one wanted Ariel and Daisy only. Well I had a devil of a time finding Ariel and Daisy, no pins inside all of WDW.
I was so disappointed until our last night there, we went back to DTD for more shopping and I met this very nice older couple (70s) in front of the pin trading circle. They had books full of pins and they had a ton of Daisy and Ariel! Since I was buying pins not trading the woman offered to go inside the pin station and pick out a few pins she wanted and I could give her those and she would let me pick out pins from her book. Such nice people.
I dont think you should only trade with CM's, just look at the pin they person is trading before you hand over your goods. Watch what the kids do a little more carefully.