Villager trades can go both ways

All trades would be listed by the item/items needed, and the emeralds given (in a range i.e. 15-30). But occasionally a new trade goven to a villager will swap the seected choice, and ask for increased emeralds (like 200% more?) . Now players can: buy ore Buy stone/building blocks Sell armour Sell tools/weapons Sell arrows Sell specific enchanting books