Now this method is combining 2 different methods into 1.
What you will need :
1. A car with insurance
3. to be in a Invite only or solo session.
Step 1. Go to LSC and make sure your car has the best upgrades you can afford at the moment
Step 2. Go to sell and confirm
Step 3. The second after it says "SOLD" press start and go to the PSN/Live store and enter it.
Step 4. Back out of the PSN/Live store
Note. You should be back in LSC ready to sell the car again...
Step 5. Repeat steps 2 - 4 (Do not back out of the sell area as, if you do you cant sell your car for a second time)
Note. After the 2nd time selling your car you should spawn inside LSC without a car. Walk out of LSC and look on your map. Your car should have spawned beside the side walk if you had insurance on it. Once spawn inside LSC without a car, you can't sell another car for another 48 minutes (in real life)
Step 6. Drive your car to the closest store
Step 7. Go into the store and rob him at gun point (Shoot or yell into your mic to speed up robbery)
Step 8. Take the money and run outside of the store
Step 9. Press start and go into the PSN/Live store
Step 10. Exit out of the PSN/Live store
Note. You should have spawn back where you were without the cops after you.
Step 11. Repeat steps 7 - 10 for 48 min.
Step 12. After 48 min, restart at step 1.
The amount of money you get will very depending on how much your car is worth. You will get around 72,000 in the 48 min from robbing the store. In addition, putting more expensive things on your car will raise the price of how much LSC will buy it for. LSC will not, how ever buy are car with a stock price of 50,000 or more. This means any car worth over 50,000 without upgrades on it. If a car's stock price is below 50,000 and has upgrades to make it worth over 50,000 they will buy it.
I suggest getting a friend or two and start a race with them and asking them to let you win. This will count as races won and the more you "win" the more upgrades on your car will you be able to be on which will make your car worth a lot more.