I think after-sales service departments are need and the simulation can be more real.
Without after-sales services, the cars, oil and some other products are awkward.
We paid lots of money to produce cars, seting up a farm, five factories, a R&D and a auto store, just sell about 100 cars and earn 1 million per month? We need to earn more, the cars we sold should be repaired.
We use oil just to produce plastic? As I know, a small plastic factory can afford all 7 cities.