I don't know how to set my chests to buy or sell certain items. Also, if you're reading this, do /l spawn FlowerCasino for the best casino on the server!

You hold an item and then click on the chest that you want to sell it in. Type the price in the chat (numbers and not for example: 1k but you type 1000) and to change it into buying you right click on it and then click on selling (it will change into buying)