Choose a spot, Click the Action Button, Select Set up Stall.
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To set the items in the stall simply drag and drop them in the Stall window and set the price. You might also sell pets, drag them from the pet menu. The items that are in the Stall window will show up grey in the Bag and Pet menu.
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After you've successfully set the stall, it will show up as your fight pet.

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When you're in game and see another player's stall, click it and you'll see his items.

Clicking a item will bring up a confirmation window, click OK and it's complete.

ALWAYS double check what your buying and its price! Don't be scammed!

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When in Stall mode you can check the transaction History.
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