When I worked in retail, anecdotally, it was my understanding that most theft was internal. At Real Canadian Superstore (think Walmart Supercenter, but not Walmart) I saw lots of my coworkers steal all kinds of things. We went through one loss prevention after another, fired for, you guessed it, stealing (ironic, I know). Most of my co workers stole their food for their meal breaks. I very rarely saw or heard of a customer being caught stealing. And no, no one reported others to management.