It looks like you're new here. If you want to get involved, click one of these buttons!
It's kind of backwards, other than the fact that they sell an item that conveniently summons a black trading post NPC next to you so you don't have to spend a few minutes walking back and forth. Outside of gem shop they're pretty rare. I think they give you a taste of their cash shop item as a story reward (Like f2P games do).
If everything else is mailed to you, why isn't this?