At the "Wonder Mail" option in the main menu, enter this code:

???J+RY??PR1
P6?JN?6T4Y?S

The code gives you a D-Ranked Rescue Job in Mt. Thunder to find a Gold Ribbon for 200 Poke. Go to Mt. Thunder, and find the wanted item. Then, before you leave the dungeon, equip it to one of your Pokemon. When you leave the dungeon, the Gold Ribbon will NOT be handed over. Then, take the Gold Ribbon from your Pokemon and sell it for 2000 Poke! The Job will still be in your list, leaving you to repeat the mission as many times as you want, provided the client never gets the item.