You can only sell loot or items/materials that you get from fighting monsters to other players. There is no NPC that you can just sell your loot to for kama. If it is a valuable resource or equipment item other players will buy it if you put it up for sale in your havenbag or a market board.

Market boards are not present in asturb

Try joining a nation and selling at their marketplaces or using the display window in your havenbag.