Vendors should realistically have defenses proportional to the value of their inventory.
- A merchant just selling food and simple weapons? Sure they can be alone and easily rob-able.
- A merchant selling valuable potions and/or magic equipment? Some combination of them being personally powerful, hiring guards, and/or having their inventory locked in a chest with a high DC to open.
Vendors in a camp/city could rely on the presence of others (e.g., aggro'ing the entire camp or dedicated city guards) to help protect their wares instead of the above. But it should still be more difficult to steal from them. An actual stealth role should be required to steal from them, instead of just hiding outside of vision cones to automatically succeed on stealth. Hearing circles - instead of just sight cones - would help fix this.
