1) Set Spawn Location to Last Location
2) Take any personal vehicle to Los Santos Customs LSC that can be sold. Mod it as much as possible then exit LSC and re-enter(to save location).
3) Sell the car.
4) Quickly Pause, go to the Online tab, then Swap Character
5) Choose your character but do not click Back, click Accept on your character.
6) You should be back in your car that you just sold, ready to sell the car again and again.
This method is undetectable by Blasterman4EVER and his righteous crew since you can use any car for this, doesn't have to be a glitched vehicle, also it puts you in a new session each time.