Technically, they do.
Bots farm adena, automated and on the best spots. They also gather materials that are either sold to players (enchants) or npc (crafting materials) all the adena is send to the storage of a bot lord (usually from Eastern Europe, Russia, but big South American bot trains on Naia). These players should all day in Giran, Aden, World Chat, Hero Voice "WTB xx000 NCoin". Where do you think these guys get the adena from to buy NCoin? Not from killing mobs in Tanor Canyon, Field of Silence or even Fafurion Temple. They get the adena from their bot trains in Pavel Ruins, Silent Valley, Blazing Swamp, Hellbound, Enchanted Valley, Plunderous Plains. Why you think zones like Pavel Ruins haven't been wiped from mobs yet, while everybody knows the bot to mob ratio is 10:1. These bots DO buy NCoins.
The real way to stop bots, is to make ALL items tradable and items in the L2Store not gift-able.