How to create a Chest Shop

This is how to create a chestshop:

S = Sign
C = Chest

S
C

Place the chest first, then above that, put a sign with:

First line: Put nothing

Second Line: Put the amount you want to sell of the item when the player buys(right-clicks) once

Third Line: If you want them to buy only, put:
B "cost" (Example: B 20)

If you want them to sell only, put:
S "cost" (Example: S 20)

If you want them to buy and sell, put:

B "cost": "cost" S (Example, If i wanted them to buy for 10, and sell for 5, i would put: B 10:5 S)

Fourth Line: The name or ID of the item you want to sell

Then your done, you can now start stocking your chest.