Nothing official have been made.
But here what I thought. There is a job system. If you are qualified for a job, it means you have join up the required guild, as I see Orussus as something well structure with the guild. So, to be able to be a merchant, you need to pay for a shop 500gp. I suppose that 500gp not only cover the building or stand where you sell, but also the fee to join the guild and the money to pay your permit, ect...
That's how I percieve it, but I have seen no official ruling in it yet.