This method got patched!
First of all I want to thank The Icon Jordan with releasing info how to earn 200K in GTA Online.
Today a new "glitch" got found out and released;
WARNING: Make a backup of your Singleplayer SAVE beforehand;
0. Make sure you have an expensive car modded
1. Start up singleplayer and start a new game
2. When the new game starts, press start and start an invite only session in GTA Online
3. Grab your most expensive car from the garage and park it somewhere close to Lost Santos Customs (LSC). Do not enter LSC.
4. Grab a nearby parked car and enter LSC
5. Go to sell and click it twice. MAKE SURE YOU DO NOT SELL IT. When it says "Are you sure you want to sell?" Press start -> LB -> A -> A (This will load up the store) and once fully loaded press B
6. Once you are back into the game and you are not in your own car which is parked outside then repeat step 5
7. Once spawned in your own car, enter LSC and go into sell and confirm the sell and you get your money (depends on which car and how fully modded it is, I got around 231K) Press start right away and then LB -> A -> A and once fully loaded press B
8. Repeat step 7 and you can do this till you get bored of it
If the above steps did not work member fromscarface found another video which works a bit different but the same outcome.
Make use of this if you want to earn money even faster since they are going to release a patch which is stated in this thread