Since Justice Points were now an important currency, the wood spirits quickly learned to use it to make the adventurers do their bidding. The wood spirits sold their special fruits that could permanently increase one's base stats at incredibly high prices and issued various quests that paid out in Justice Points. This made the "greedy" adventurers eagerly work for the wood spirits.
At first, perhaps there were a few quests or items that paid out or were priced in an unbalanced manner, but I believed in the self-correcting power of the market. As long as there was a sufficient amount of Justice Point exchanges, things would balance themselves in the end, just like my original world's international markets… and if the Justice Points exchange system didn't balance itself and ended up going bankrupt, then it wouldn't be my fault!