Anyone can own a shop. There are however two requirements while owning a shop.
1. A description of your shop and the shops location.
2. A list of wares. and prices.
Wares don't just pop out of nowhere though. So wares must be gained in a number of ways.
1. Getting stuff from missions.
2. Synthesising items.
3. Buying from the merchant's guild.
4. Buying from adventurers.
Each shop owner gets a nice starting fund of 1000.