These are the people who will evaluate your progress in their respective guilds, Talking to them at level 8-10, 18-20, 28-30, 38-40, 48-50, 58-60, 68-70, 78-80, 88-90, 98-100, will result in an item request. Trading said item will result in an increase in rank for that guild, which allows for access to more special crafting items as well as the ability to level your craft further (if for example you don't hand in the item for lv8-10, you can't progress past 10 in that craft)