Bartering can be leveled by trading with villagers, exchanging emeralds for items or items for emeralds, just like vanilla MC! Each level of bartering adds to the trades you have unlocked. This mainly affects the EcoEnchants custom enchants, as well as some items. You'll need to level your bartering skill in order to be able to trade for rarer custom enchant books with your librarian villagers!
Bartering gives you increased saturation, wisdom, and boss fortune, although boss fortune is disabled on PrismaCraft as of 8/21/2022
Bartering also adds a message when hovering over the red X in the trade menu, letting you know that villagers will restock up to twice a day, meaning in game day. This is still affected by a player completing other trades the villager has to offer!