Hes right, Dupes are the best way. It's endgame gold in gta. Just gotta be smart.
If you and your friend get a casino heist with big con and paintings you can do a back to back and make 1-1.3mil every 20-30min, and since it is a back to back glitch you can do it constantly without having to redo the setups.(you will have to give your friend the highest cut you can bc you won’t be getting any money)
I say vehicle cargo but top range since it gives you 100k for high end modifications