Don't listen to him. I've got a better idea
Well, if you already have purchased several mystery cars and you are afraid of getting any duplicates, then go into the Hot Wheels aisle of the supermarket/store/whatever-the-hell. When no one is looking, slightly tear open the mystery package. Not all the way, just a little so you can get a good look. If you already have the car, leave the package alone. If you don't have it, take a quick look around and place it in your pocket. Hot Wheels collectors everywhere do this.