It's pretty easy actually.
You gotta have a 2nd character with a garage (gotta get to rank 5), doesn't have to be the same garage
Basically, you just kill yourself and swap characters at the same time.
Detailed:
Go to your first character (who has all the cars), and do the kill yourself thing
As soon as your gun goes off, go to the start menu -> Online -> highlight Swap character (don't hit it right away)
Then when the screen goes black (from killing yourself) the menu will still be up and you hit A about 3-4 times. Timing is crucial, you gotta let the screen be black for like half a second, then hit A.
So when you do that right, this weird transparent pop-up screen will show up that has "Quit" on it twice, you hit B when that shows up.
Then pick your 2nd character.
Another weird transparent screen will show up that looks like the top of the pause menu, hit A on that.
Then when you come back, all your cars from your 1st character will be in your 2nd characters garage as well.
Before you sell the cars tho, you gotta paint it a different color so it doesn't fuck up and delete the car from your 1st character as well.
After that, you good. You can sell them back-to-back, supers, no wait limit. Still gotta wait on the mechanic.
I've been selling 4 supers at a time (2 adders, entity, stinger), and then restarting the glitch. I make like 3 mil just off those 4 cars every 10-15 minutes.
