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.
We've recently instituted a new practice. If you want to sell more than 100 comms to us, or any amount of particularly comms, you'll need to message Verrucht. He'll handle the transaction. This way, we won't have someone depleting the treasury by unloading 20,000 coal or anything else we don't need at the moment. There's a poster in our commshop that explains what to do.
I will agree that setting per person limits might be worthwhile, but primarily that's still just addressing a user error on the part of the person setting the prices. If you have set a favourable price that will encourage people to empty their rift of a particular commodity, that should mean that you want as much as they can sell. If you do not, make sure to set your price accordingly. These functions already exist within the current system. Those who sell to Cyrene on a regular basis know to approach me personally if they want to sell in bulk, since I can actually withdraw and buy in larger quantities for things that we actually need.