Really? I've never heard of that before. I've heard that they trade regardless if they can tell if they are scrappers or not. That's why when you go on eBay and look at the lots that you can buy (i.e. 50 pins for 20 bucks) they are always sold as "trade-able". Because the CM's aren't allowed to say no due to the fact that they are scrappers.
Also, from what I've heard, a lot of the pins on the lanyards are already scrappers from previous trades. I don't think they refresh the pins. When I did the Backstage Magic Tour and went into the Utilidors, there was a room that the CMs would go in to pick up their lanyards. They made it seem like it was a room with a bin that you place your lanyard in when your shift is done, and pick a lanyard up when you start your shift.
I'm not a CM though, so maybe I'm wrong?