-Play Dragon Adventure mode until you reach the ‘Two Majin Buus’ storyline during the Majin Buu saga. As Fat Buu, head to the top right area of the map to the Mountain Road area. Yamcha will be there offering you a contest to see who can last the longest in a fight. If you’re able to defeat him or survive, he’ll reward you with 1,000,000 Zeni as well as Equipment Slots +4 and the Fox Mask fusion capsule. Repeat this to gain lots of money. Note: be sure to increase Fat Buu’s attributes so you can beat Yamcha quicker.
-Replay the event ‘Mysterious Alien Warrior’ to unlock the hidden saga ‘Fateful Brothers’. As Raditz keep battling against Saibamen to earn green Z-Items called Saibamen sets as well as Zeni and XP. Saibamen Sets sell for 150,00 Zeni at Baba’s shop. Repeat this as many times as you want.
-Fight the thee training Saibamen in the wastelands during the ‘Tree of Might episode. After the fight you will a Saibamen set, which can be sold for 150,000 Zeni. Repeat as many times as you want. Note: The best time to do this trick is during later sagas when you have stronger characters such as Super Saiyan Trunks or Super Saiyan 2 Teen Gohan.