Same for those moving sidewalks at airports. You'd think the large signs (walk left, stand right) would make a difference, but of course not.
Funny they thought you were a CM. As long as you sound official, how would they know unless they turn around? I bet it's an interesting reaction discovering you don't work there after complying with your instructions. Once, years ago, I was given a 20% discount at Target and didn't understand why until later I realized that I was wearing a red shirt that looked very similar to Target employee shirts. Crazy. I guess that cashier just assumed and hit the button. (unlike disney where you have to produce the discount card, ID, blood sample, SAT scores, and your elementary school GPA to get that 10% you're entitled to.)