They need to I pliment jewels directly into the game so people playing must continuesly purchase them to keep playing or simply sell what they find in game. Everything in game should use jewels not in game currency or at least trades between players or auction house should be done with jelwels.
It is not a good idea if the player use jewels to buy the items directly. Ingame economy profits more if the commerce are done indirectly.
https://www.youtube.com/watch?v=fKK9nVLvhGM