To add a shop, all you need to do is clone an existing location (if it isn't there yet), add a shop-character and copy a dialog file for him. Some shops (Saint Martin and Antigua) have randomly generated shop-owners. The same goes for the taverns. Sometimes there is an owner, sometimes not. And it's a different owner each time. This is CCC's work to have the shops being occupied automatically without having to manually put anyone in there.