As a kid, there is a beggar in the Hyrule Castle Market that asks you to sell him things with C. In the future, that same beggar is relocated to Kakariko Village, which is perfect for arguably the fastest non-Skulltulla money trick in the game. Behind the old lady's potion shop in Kakariko lies a grotto that contains a fish. Bring a couple of empty bottles to the grotto, then enter and re-enter the grotto until you're able to fill all of your bottles with fish. The beggar will buy each fish for 100 rupees. Repeat this process as many times as you wish until your money is maxed out. This obviously works best when you have the Giant's Wallet and can carry a maximum of 500 rupees at a time.