Ok so your looking for easy money. We all know you gotta work at getting that bank on the new gta 5 online. Alright lets start by saying doing this glitch may cause you to be put into a bad sport game even though I haven't heard of any one getting this unlucky it may happen.
So go ahead and get on online options and change starting location to last location not home or garage. Take your best car you can sell and upgrade as far as possible. Now take the vehicle to the mod shop, once inside repair or whatever.. if you put any mods one you will want to exit and reenter. Ok so push sell, its gonna ask are you sure, push sell again, it will say sold. Now pause, goto online, then swap character. Once in character push your character and your back in the game with both car and money.
Warning- do not try after beach bum update. To test use a random car off the street. Have any questions just ask. I check the web site daily.