You may have to be a premium member to create a shop. Or maybe you have to be staff. I'm not sure. I know those who can open stores can hire people though. XD
You know how in PMD2 you can find those boxes and xatu sees what is inside of them? In your site on certain explore pages you would see a box/treasure chest and you can go to some kind of creature to appraise it. (It would be free to appraise and when you appraise you would get ether some site currency, items (when the item mod is made), and maybe some other prize?) The boxes wouldn't reappear in those places for a week and they would have a different reward. (Though certain boxes could be special and you can only get them once/always have the same reward in them and appear at the end of a place or something)