Auto makers often sell one model of car in different trim levels at different prices.

In this practice, what do auto makers try to do essentially?

After purchasing a new vehicle, car dealerships often offer the customer a "Value Package" that combines several maintenance services such as oil change, tire rotation, brake service, and other regular check up etc at a discounted price. The customer can purchase those services individually at a higher total price. What do car dealerships try to accomplish in this offer?