The Dyescape shop system allows you to purchase and sell items from and to a Merchant NPC. Every shop NPC will have a Merchant title above their head. This is how you can indicate that the NPC you see is a Merchant NPC. To open the NPC shop, right-click the NPC.
When opening the shop after clicking on the NPC, you will be prompted to the main shop menu. In here, you see a list of items. Each and every shop may offer you different items, and for different prices (more info below). You can use the left and right arrows at the bottom of the shop to scroll through the pages of items. Hover with your mouse over an item to check it out like you normally would. At the bottom of each item, there is a green message stating the per-item price. If you wish to purchase the item, click it.
After clicking on an item, a new menu will be opened for you. The item you just clicked will be rendered again in the middle. You can use this to confirm that you clicked the correct item. Next to this item, there's 2 buttons on each side. A -1, -5, +1 and +5 button. These buttons are used to increase or decrease the quantity of the item you're about to purchase. Clicking the +1 button for example would raise the item quantity by one (by default it's set to 1). After clicking this button, you will notice that the item in the middle will raise its quantity. You should now see a 2 under the item. This means you're about to purchase the item twice. The other buttons work in the exact same way. Clicking +5 will increase the quantity by 5, and clicking -1 or -5 will decrease the quantity. The minimum quantity is 1 and the maximum quantity is 64. If you wish to purchase more than 64 in quantity, you must purchase a stack of 64 and repeat the entire flow again until you have the quantity you're looking for.
To finalize your item purchase, you can click on the big green Purchase button on the right. When hovering over this button, you can confirm what you're about to purchase. When hovering over this button, you will see the item name, the quantity and how much this would cost in total. If everything looks fine and you want to finalize your purchase, click the button and the items will be added to your inventory.
To cancel the purchase, you can either click the big red Cancel button on the left, or click the Back button at the bottom left. Both buttons will cancel your purchase in the exact same way.
You can also sell items to a shop. If you wish to sell items to the shop, right-click the Merchant NPC and click the Sell items gold coin button in between the two arrows. This will prompt you to a menu where you will see an exact representation of your inventory. When hovering over these items, you will see a green text at the bottom stating the per-item sell price. When clicking one of these items, you will be prompted to a similar menu just like the Purchase view. Your item you just clicked will be displayed in the middle for confirmation and there are two big buttons for cancelling and confirming your action, as well as 4 buttons to control the quantity of the item you're trying to sell. The minimum sell quantity is 1 and the maximum quantity is defined by the quantity of the items you just clicked. For example opening this menu and clicking a stack where you have 34x Zombie brains, the maximum quantity for selling this item after clicking on it will be 34. If you have items spread across multiple stacks, you will have to go through this sell action for every stack of this item.
Similar to the purchase menu, when hovering over the Sell button, you can confirm what you're about to do by reading the text prompted to you. It will display the name of the item you're about to sell, the quantity and what price you will receive for selling those items.
When purchasing or selling items from and to a shop, you may have noticed that prices may vary between them for the exact same item. This is because every shop has a (or multiple) class and an (or multiple) item type associated with them. The combination of these classes and/or item types define what the NPC Merchant is interested in buying from you and what he prefers to sell to you. When selling an item to the NPC Merchant which it is not interested in (for example selling a Mage wand to a Knight/Warrior armory shop), the price offered to you will be significantly lower because the NPC prefers to not buy those items. When trying to sell the exact same items to the correct Merchant (for example a Wizard shop who sells Mage weapons), you will get the best price offered for your item.