Head to the market, right under the toribash banner at the top part. Once you have done this, you will see on the left side your inventory, click activated or deactivated depending on where is the item you want to sell and click the image of the item you are going to sell. You will see a label named "price", simply set the price you want and click the update button.
Remember to check the market first in order to see if your price is reasonable according to the other sellers.
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