With the advent of the Delos comm market, it would seem the utility of city commshops is severely diminished. One of the biggest challenges during the mining era was runs on certain commodities. Now that the prices have stabilized somewhat, I think we can revisit it a bit.
I think a couple things would help trade:
Have them function somewhat like regular shops in that you can refuse service to certain people, grant favorable or unfavorable prices to others. This would allow it to be a service to the city.
Having some third person message when you look at the commodity shop indicating it is out of funds. Just would improve general quality of life and allow us to pass it along to the minister rather than having to pull something out, drop selfishness, and try to sell it.