Honestly, it's probably harder to shoplift with the attendants personally escorting each shopper.
I've shopped at a couple places during blackouts, and while I didn't have shoplifting on my mind at the time, I recall they asked you at the entrance what department you were going to and what you were buying, would just take you directly there, and then walk you immediately back.
Now, if you were standing in front of a box of diamonds when the lights went out... that's another story.