NOTE: Make sure that you have A LOT of catch cards!!!
Once you get lots of catch cards, go to Chapter 5-2. Once you enter the chapter, just keep going until you reach the place where the yoshi statue is. Then, flip into 3-D and head back toward the edge where the moving platform is. You will see the rare Amazy Dazzee! Now, use one of your catch cards on the Amazy Dazzee. Once you trap it inside the card, use the Red warp pipe in the Important Items to head back to Flipside. Go to the card shop. When the store owner asks you hat you want to do, press "sell". Then go to the Amazy Dazzee that you caught with the card and sell it to him. Just say YES and and he'll give you 300 coins! And now, go back to Chapter 5-2 and keep repeating the process until you have maxed out your coins!