How to Make Easy Money in Pokemon Sapphire

Defeat Normon, the Petalburg Gym Leader. This is part of the storyline in Pokemon Sapphire, so you cannot miss this fight.
Return to Littleroot Town and talk to your mother. She will give you the Amulet Coin.
Equip the Amulet Coin to one of your Pokemon.
Talk to Gabby and Ty on Route 111 to start a battle. These two trainers will move to Route 118 after you defeat them. You will receive substantially less money the first time you defeat them.
Talk to Gabby and Ty on Route 118 to start a battle. Defeating the trainers will cause both to move to Route 120.
Talk to Gabby and Ty on Route 120 to start a battle. The two will return to Route 111 after you defeat them.
Talk to and defeat Gabby and Ty on Route 111, Route 118, and 120 again. This will cause their Pokemon to reach their maximum level. This will in turn cause the amount of money you receive from defeating them to increase substantially.
Defeat Gabby and Ty whenever you need more money. You will receive $7488 each time you beat them, as long as the Pokemon with the Amulet Coin wins the battle. The two will keep rotating between Route 111, Route 118, and Route 120, each time they are defeated.
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How to Earn Game Coins in 'Pokemon FireRed' and 'Pokemon LeafGreen'

Walk to the row of green houses on the southern-most edge of Celadon City and enter the building on the far left end. Talk to the man in the top left corner of the room and he will give you a Coin Case. You cannot collect Game Coins without this item.
Enter the large orange building in the center of town. This is the Celadon Game Corner.
Talk to all of the patrons inside the Game Corner. Some of them will give you Game Coins.
Press the 'A' button with each step you take to search the floor for Game Coins.
Face a slot machine and press the 'A' button to play. Press up or down on the control pad to wager more coins on the slot machine for a potentially higher payout. Pushing left and right on the control pad increases your chances of winning by giving you more options for the icons to line up. Increasing your odds lowers your payout if you win, though.
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