Use the highlighted /shop signs at Spawn to buy items or sell items to the server. These are separate from player-owned chest shops and the NPC traders at /warp shops.
Each sign shows the item, trade amount, and the price for each action it offers. Right-click to buy; left-click to sell. Some signs only buy or only sell.
Have enough money and room in your inventory before buying. Carry the items you want to sell.
Normal clicks trade the sign's listed amount. Sneak-clicking trades a full stack if that amount is 1, or one item if it is higher.
Check the sign's current price before trading. For stock-priced items, buying reduces stock and raises the buy price, while selling adds stock and lowers the sell price. Some items use prices that are not affected by stock.
/warp shops and the Adventurer's Guild.