It might be different in other states, but this is definitely not common in Colorado.
Most of the people who work in shops as budtenders, store managers, etc, are not people that you would want to have guns, nor would they want to carry guns.
Most of the time the owners aren't working in the shops themselves, so you don't see them packing guns either.
Most medical stores are pretty well protected. You have a locked outside door with one or two cameras. You then get buzzed in to a secured area where you show your state ID, your medical card, and sign a log. The patient(s) are on at least two more cameras and you are typically passing your info through a slot to a person who is behind bullet proof glass.
The medical industry sees a good number of burglaries, but not robberies. The burglaries are somewhat unavoidable, but most of the time it's limited damage.
Even in this case the guy wasn't abducted at work but at home, and by a friend. No concealed carry is going to help there.