During gameplay, when you win something, the machine will pay out the prize immediately. With this cheat, though, you can keep your prize inside the machine as a credit. To do that, before inserting the coins, press Start and immediately press B once (don't hold it) on Controller 1; this will not only show you the money you just won, but disable the payout for the next win. You need to do this trick every time after winning to keep all your prize as a credit.