Ok let me just say this. While this sounds all fine and dandy this wouldn't be entirely fair for the whole player base to have player owned shops. Let me explain why. Just because you can do gfx and make stuff doesn't mean others can or even have a pc to be able to make the items. There for how would this be fair for the people that don't have the ability to make items and own shops? It wouldn't be fair for a certain amount of people to gain a profit off making things when others can't.
I'm not trying to complain or attack any one just simply laying out why this may sound good but cant happen because its not fair for everyone. If you want to earn gralats for making items go be a gfx admin.
The only way this kind of thing would work fairly is if players could select items and purchase them at lower cost then sale them at there normal retail value in their houses. Which is how the real world stores work,but if you do that then your making the all ready in game shops essintally useless. So player owned shops aren't going to happen.