Bukkit

To create a shop you need the permission xpShop.create or xpShop.create.admin. Then you have to place a sign. It should look like this:

If you want um create a AdminShop:

If a player shouldnt be able to buy or sell on a Shop set the sell price or the buy price to 0.

Then if you have the permission xpShop.use, you can hit the sign and buy if the seller is online or it is a AdminShop or do a left klick on a shop to sell.