This is a post by Yoman35 from se7ensins, apparently it seems to be working, he simplifies ReflectedTACO's method by skipping unnecessary steps.

Step 1: Start a NEW singleplayer campaign (I would recommend manually saving your real one)

Step 2: After the "Nine years ago" screen, hit start and open up a new multiplayer invite only session

Step 3: Grab your car worth 50k+, and park it close to, but NOT inside the customs shop

Step 4: Leave the car, and go find any other random car. Drive said car into the shop

Step 5: Hit the sell button TWICE, but do NOT confirm the sale. Directly after you hit it twice, push START, L1, X, X, and then the PS/XBL store will come up. Once it appears, hit O. (Xbox buttons are LB, A, A, then B)

Step 6: Once you come down from the shop you should still be in the random car in the shop, repeat step 5, otherwise skip to step 7

Step 7: You now should come down into YOUR car sitting outside the shop, simply drive into the shop and you should have the option to sell it.

Step 8: At this point it should be the exact same as the bike glitch. You can sell your car, go to the store and back, and you will keep spawning in your 50k+ car.

Step 9: Rinse and repeat until desired amount is achieved