I wonder if it might be possible to add a feature that would allow players to create their own MarketZoneSpheres.
For example:
Player builds a station somewhere, and labels one or more of his cargo containers to contain the string [MarketContainer]. This then allows players to establish their own shops.

To further elaborate;
Player Derp could purchase a "Merchant License", which grants them a separate "Merchant Account" which they may name and transfer funds to and from at will via chat command.
For example: /license "Derp-Mart" would create a merchant account belonging to the player, under the name "Derp-Mart". A licensing fee would be subtracted from their balance, and then they would be able to /deposit 500 "Derp-Mart" or /withdraw 500 "Derp-Mart" in order to transfer funds between their Merchant Account and themselves.

For simplicity sake, Merchant accounts could be limited to one per player.
Any container belonging to Derp that contains the string [MarketContainer] and any other containers attached via conveyor system all count as one instance of a MarketZoneSphere for "Derp-Mart".

Derp could then dictate what to buy and sell from that container by using syntax such as:
"Derp Ore [MarketContainer] {Sell Ore}" curly brackets tell the container to freely sell the ore contained within at the existing market prices. Optionally, he could use {Sell "Iron Ore" 0.50} to specifically sell any Iron Ore in the container at 0.50 per unit. or {Sell "Iron Ore" 0.50;Buy "Iron Ore" 0.45}. This particular container would only deal in Iron Ore with these options, unless Derp were to name the container with {Sell All; Buy All}.