npc universe trader buy most if not all goods for -1 of the average price for the product you're selling. now this of course isn't the best and most profitable way to sell your goods.

yes there is the command "sell/buy ware for best price" which a ship of yours can execute once you have assigned your factory as the home base for that ship.
depending on how you adjusted the pricing and maximum jump range for your factory, your ships will buy/sell resources/products of your factory.
you also have to deposit some money onto your stations bank account, because your resource shoppers strictly work with that account and not your global player balance.

ore and energy cells are in high demand in certain core regions of the universe, but you can also sell food products.

for this command to work you don't need to have satellites in your business sectors, however you must have uncovered the stations previously for your ships to know of their existence and of course you need a good enough relationship with the race who operates those stations in order to be allowed to dock and do business.

thanks :)