Used Car Salesman
From Halopedia, the Halo wiki
Used Car Salesman is a Halo 3 achievement. It is awarded for destroying a vehicle with 3 enemies in it in either online or campaign. Unlocking this Achievement gives you the Scout Helmet for Spartan Armor customization. Though there is a campaign glitch where you destroy a phantom's turret with a Machine gun turret.(rarely happens)
Note
The vehicle has to be completely destroyed with all the people in it. Ex. If you shoot a rocket(SPNKr) at a Prowler and kill all the people on, if the vehicle isn't actually destroyed (you can still ride it) you will not get the achievement.
