First, you might want to just email the seller and see if they even know that it's broken. Duh, you already did that.
I took a look at their feedback, and it looks like they are a casual seller. Not everything they are selling is pins or even Disney. Yes, there are pins but it looks like someone is selling a small collection. It's always possible that they got the pin off a CM lanyard and it was already broken and if they don't know about pinpics, so never knew it wasn't complete.