I worked in retail as a college summer job and someone let their cart loose and it cracked a light on my car. The security tapes confirmed it. I was parked way off to the side with the other employees and the cart gained some momentum on its way.

Another similar test is when someone changes their mind on buying something if they return it to its original spot or just dump it on a random shelf. This is another thing that I really hated dealing with in retail.