Instructions
Defeat the gym leader in Petalberg. Return to your mother at your home to receive the Amulet Coin. The Amulet Coin doubles the amount of money you receive when equipped to a Pokemon used in battle. Place it on your primary Pokemon to ensure that you always earn twice as much money.
Use your Pokenav to save high-paying trainers. The Pokenav allows you to save trainer locations in the game and alert you when they are ready for a rematch. Pull up the Pokenav and look for flashing Pokeballs on the map. The flashing Pokeball indicates that they are ready for a rematch.
Fight the Elite 4 with the Amulet Coin equipped. You can redo the Elite 4 battle an unlimited number of times, and they are the highest-paying trainers in the game.
Locate Rich Boy Winston in the forest next to Petalberg. Equip the Amulet Coin and a Pokemon who knows the Thief move. Use Thief to steal the gold nugget his Pokemon is holding. Nuggets are worth $5,000. With the Amulet Coin equipped, he gives you roughly $15,000 in prize money. Add him to your Pokenav and fight him as often as possible.