Clans can purchase an Office in any city as long as they have 100 or more Ji there. The cost of the Office will rise with each Office purchased.
Only the clan leader or sub leaders have access to the clan office, however, they have the option of selecting another clan member to be a local officer. This officer will also be given access to the Clan Office to help manage the city. There can only be one Local Officer per city.
Having a clan office is also a requirement in order to start Clan Battles.
Having an Office allows clans to sell items in the local Shop. The higher the local Ji a clan has, the better the items they can stock in their shop. Clans will purchase items in lots of 10. The cost of these items will be 1/4 of their actual value. As people buy the items, the clan's supply will decrease (ie, if a clan has 6 swords available and I buy 1, they have 5 left). At every 100 Ji, a single new item will be made available for clans to stock, until all items available in that city can be stocked. The order in which the items become available will be unique in each city and won't necessarily be in a sequential order. For example, if the city's shop is known for spears, you could get the 4th or 5th spear before you get the 2nd sword. It also won't simply just be 'spear, bow, bludgeon, axe, sword, armor, knife, shield, spear, bow, bludgeon, etc', but a more varied order. When stocking an item, you can see how many of that item are currently available in the city's shop, but you can decide to stock something another clan already is. A little competition is always good.
Clans will be limited to 10 'slots' for stocking different items in each of their shops, with the limit increasing by 1 for every 500 Ji they earn there. So if they have 10,000 Ji in an city, they'll have 30 slots. Each slot can hold no more than 10 of an item, but clans can put the same item in multiple slots. So if you want your clan to sell nothing but Sharpened Sticks, you could get 100 Sharpened Sticks in a town by filling 10 slots with 10 Sharpened Sticks each. This is useful if you have a popular item not yet available in other shops and don't want to run out.
You can only stock another item if you have a slot available, regardless of how many actual items you have available. You may just have 1 each left in each of your 10 slots, but you can't stock anything new until a slot is free. You do have some options though. If you have some stock that has been sitting on the shelf for a long time and just won't sell, you can sell it directly for half of what your clan paid for it. This will free up the slot and allow a new item to be stocked there. If you simply want to restock the item that's already there (fill it up to 10), you may do so, but you won't get as good of a discount as you would for buying 10 in bulk. The cost will be whatever it would be to buy 10, minus about 1/8 the value of the item for each item you already have stocked in that slot.
Additional slots can also be purchased by buying City Upgrades.
For more info on what items are available where, please visit the Shops page.