Say you've got your re-usable bag(s) full of stuff (I use another plastic bag on top to conceal the items) and you're about to pay for the items that are on the normal part of the trolley and you're adding your items to the checkout. At this stage, do you think they bother observing you? You are about to pay after all. I always feel like i'm being watched right until the very end, which I'm sure is perfectly normal.
Checkout is probably the easiest place to watch people.
Watching 10 lanes of checkout vs 20 isles or wtf ever of sales floor is a lot easier.
"Pretending" you are buying something and then stashing that sick PS69 game cyberchad 2420 up your butt is also something I would figure lots of people would think makes them more inconspicuous. If I was LP I would hella watch the check out lines.
They watch self checkouts. I would just push a cart out.