design/tunes/logos on the storefront is decent, designs and logo cost nothing besides time and it's really not that hard (I can't draw AT ALL in real life and I'm pretty decent at logos and racing replicas, these sell well).
I hate the idea of having to actually "grind for money", I want to spend most of my time playing the game. So I accept to spend some time early on to replicate logos and cars (plus with time it gets fun), and then, everyone I turn my game on, I get between 50k and 400k. I don't race career (I hate it), I only spend my gaming time racing online, hotlapping/tuning (same time) and doing just whatever I want whenever I want.
I allways refused to do something I didn't want in this game, and allways found my way around it "legally" (never used a money glitch)
actually, the best way to make easy and fast money is to play 100% of the game's features (design, tuning, storefront, auction house, racing) you enjoy yourself 100% doing just whatever you want.
I see many people never use their storefront for sales, even less people use the AH these days, but that's where the money is if you play it right.
Storefront Keyword (tunes): Yamadatuned
Classic JDM designs, low class grip tunes, vynils groups, kaido replays and photography.