Selling crafting skills?

ChidoriNeko - Lost City

okay, i've looked im some guides about selling crafting skills but no one posted anything about it. i dont feel like going back in pages to search everything so i'll ask.

i've seen people sell their crafting skills to other plays and im wondering how could i do that. seriously, i dont get it. i have lvl 3 blacksmith anyway..

Asthariel - Dreamweaver

The books you get from completing crafting quests for certain lvls such as lvl 4, lvl 6 and I think lvl 8, are sellable. The items you get from cashshop that lvl your crafting skills are sellable too.