For myself, I enjoy printing money out of thin air by crafting outfits.
Each of the non-candidates, throughout the story, you will obtain a recipe that allows you to create versions of their palette swap costumes that retain their normal hair color. Works great for some outfits, others are nice enough with the new color. After you make one, you can buy more at a whopping price of 2.5 million credits - which in turn means the selling price for these custom outfits is 1.25 million credits. That's right. Not 125k or some otherwise expectable number. One and a quarter of a million shiny credits.
This is how the process turns into printing money. The recipe for any given custom outfit is the normal version of that outfit, plus an Invisible Cloth. The cheapest outfit for any given non-candidate is 5000 credits. Scouts can gather Invisible Cloth at mid-to-high payouts when exploring Castle Chambers in Lowee, or at most payouts when exploring Suaho Mountain Range in Hello Continent - set some of your better item collection scouts (Stamina is the stat you want) on auto-dispatch there to just harvest as you continue in the game. Alternatively, you can just manually collect them from the ghosts in Suaho Mountain Range yourself - if you just take one stroll across the dungeon (probably with Gather Shift, Gather Shift +1, or a Drop Rate scout bonus), you can probably pick up 3-6 of them without needing to retrace to a respawned foe. Plug that in and that's 3.75 million to 7.5 million credits in a single run. More if you feel like lollygagging.
Castle Chambers is available in the middle of Chapter 3, while Suaho Mountain Range is available at the very next chapter from the get-go, rendering this printing press of fortune even an early-game strategy. Who needs to win at a quiz show with this much income?