On the topic I'll post a guideline on how to successfully make a shop and use it.
How to make a Shop
• Place a chest on the ground
• Place a sign 1 block away from the chest (i.e above it, in front of it by holding shift etc.);
First line of the sign will be filled automatically by your name
On the second line you write the amount of blocks they receive for a specified amount of money
The third line is the price line. You need to have a price indicator (like 'B' - price that will apply to items BOUGHT by PLAYERS - or 'S' - the SELL price) near the price. You can also combine them by separating the prices with a colon (. Some of the possible price combinations: "B 10:5 S", "B 5" etc.
The forth line holds information on what the item being sold is. You can find out the name of the item you're holding by doing /iteminfo
This sign indicates that a player is selling 10 Iron Ingots for 70 Krunas.
This sign indicates that a player is selling 64 Quartz Blocks for 90 Krunas and that they are buying 64 Quartz Blocks for 50 Krunas.
Commands and Usage
• You can right click to buy from a shop and left click to sell to a shop.
• By default once you make a shop you will be notified (if you're online) if a player bought from your shop. To toggle those messages, you can do /cstoggle
• If the first line says Government Shop or Government, it means you can buy from/sell to the Government. (The Government Shop is found at /warp GovernmentShop where you can buy/sell resources!)
• In case you're selling customized items, such as enchanted items, written books, banners, enchanted tools or renamed items, you need to do /iteminfo whilst holding the item for the exact ID for that item.