The Wang Cars side quest can be exploited for more money and additional reward cars. To do so, save the game with at least and ideally one GT-A1 remaining. Once you reload the game, all eight GT-A1's will respawn. Now you can collect any one of the cars to complete the quest regularly and receive your rewards. For each of the additional respawned GT-A1's collected after that point the game will reward you with another $200,000 and an additional set of reward cars on the streets surrounding the Wang Cars showroom. Doing so for all respawned GT-A1's adds up to a total reward of $1,600,000, over half the money required to unlock the Industrial District.