I was in Walmart a few weeks ago waiting to check out and the clean-cut couple in front of me were paying for their items. The guy finished paying and the woman quietly said to him that they had forgotten to pay for a large container of laundry detergent that was still in their cart. The guy just motioned for her to be quiet and they walked out of the store with both their paid groceries and the unpaid item.
My wife was with me and when I started to say something, she asked me not to make a scene. I then asked the clerk if he knew that they had not paid for the item and he either ignored me or didn't understand me (remember, this was Walmart!)
I wanted to at least tell the clerk at the exit doors but my wife asked me again not to say anything. I was carrying at the time, but it never entered my mind that this was a potential issue. I now realize that any confrontation has the potential to escalate. I still feel I should have said something, but I also understand that with the license to carry comes a responsibility to behave responsibly. Since I am armed, I have to look for ways to de-escalate confrontations, not escalate them.