Career Requirements
In order to unlock Tier 3 and its better cars in Need For Speed Undercover you must log in to the game's career mode and complete race "jobs." Each job specifies victory circumstances that give you credit for winning the race and completing the job. Available races appear on your game's GPS map. Each time you complete a race you progress through levels and earn rewards such as cash, cars and items.
Tier 3 Car Shop
Before you unlock the shop where you can purchase Tier 3 cars you must complete races until you reach Level 5.3. Once you are Level 5.3 and you complete a race job then the Tier 3 car shop is unlocked. After the shop is unlocked you can buy the base version of all Tier 3 cars in the game.
Free Tier 3 Car
Once you reach level 8.5 start and complete a race job. One you complete the job then you will win a free Tier 3 car. You will be given the option to select from any Tier 3 car that you have not already purchased.
Upgrade Shops
Twice during the game you can unlock an upgrade shop that allows you to improve your Tier 3 cars. Once you reach level 7.5 you must complete three jobs to open the race parts shop. At this point in time you will only have access to Tier 3 cars and lesser, so the shop is your best bet for improving performance. When you reach level 11.5 then you will gain access to a more expensive, more effective pro parts shop. You can use this shop to augment any Tier 2 or Tier 3 cars that you own.