It's great to hear others stories when it comes to our children trading. My DS is 4 now (on Feb. 11) and we both started our pin trading on the 5th of Feb. when we made a "mother/son" trip to WDW. After seeing the DS pins and how people had posed that they were trading them at the parks, I thought it would be a great way to get some souveniers without spending alot for them. Once I was there, it dawned on me that this could be a great opportunity for my son to "come out of his shell". He's a little shy, and won't talk to strangers at all. So when we started trading I was doing most of the talking, and by the time we left he was sitting in his stroller, riding along and I'd hear "Mom, pins mom. MOM! PINS!" That was for every CM I'd pass, not paying attention to what they had around their necks because I was dodging people and strollers trying to get to the next attraction.
We had a great time trading with the CM, but we didn't do any trading with other guests. Maybe in September when we go back it may happen, and I hope we don't encounter any sharks trying to take advantage of my son. It's sad that there are those in such a magical place that would try and do that, especially to a child, but I appreciate the "heads up" to watch out for the sharks.
Good luck on your next trip, and I hope it brings better meetings with other guests.