I like the idea of having a shop at FC. FC's with shops inside could have signs outside displaying their status. Additionally the sellers should be able to list their wares on the global market and the buyer can be given an option to pay for the delivery of the item or go pick it up him/herself. I think this would satisfy both roleplayers and non-roleplayers.
Part of the tax paid on these sales or all of it should go to the FC.
And I also think that we should be able to limit to who we sell our wares on these retainers.