Where's My Car? Achievement
Where's My Car?10
Deliver all the cars to the chop shops
Chop Shop, as well as Hitman, (see "Hello 47") is different from all of the other activities. When you go to a Chop Shop location, you will be given a list of eight cars people and where to find them. When you enter any of the cars, as long as you aren't in a mission or activity, the game will tell you that it's wanted in a Chop Shop.
Simply drive the car to the nearest Shop to get credit. If you are in co-op, your partner must be in the car to get credit.
For additional help, check this thread.