I've had two similar experiences, user, both of which were deeply unpleasant.
The first time I was on my way home from work. Having missed my bus I browsed around a little clothes shop, found nothing of interest and went back out to the bus stop. I heard shouting behind me but thought nothing of it until a young man grabbed hold of me and demanded my bag - I thought he was trying to mug me until he shouted that I'd stolen something and needed to give it back. I showed him the inside of my bag, then he demanded I take my coat off too! This was in rush hour, there were dozens of people around staring and judging me. When I proved I had nothing to hide, he said I'd gotten away with it and banned me from the shop. So I saw red, followed him back and demanded to speak to the manager... who gave the young man a sharp shrift because he'd accosted the wrong person. The woman in question was stood laughing at us across the road!! I got an apology right away (and a cup of tea), but it still really shook me up.
The second time was much more unpleasant.
I'd popped into a well-known supermarket's "express" store (the type where you can only park for 20 minutes) with DS, who was about a year old. Rather than get his pram out of the boot, I decided it would be much easier to carry him I only needed a couple of things.
As I was having my shopping rung up at the till, a female security guard came from the back room and stood next to me. She asked if there was anything I'd forgotten to put in the basket. I replied that I'd not, and checked to make sure DS hadn't picked anything up (which he hadn't). She then asked to see in my bag. I offered it to her to look at (as I was holding DS on my hip) but she said I had to do it for her. So I sat DS on the counter and emptied my bag on the floor.
As if that weren't enough, she told me that she knew I had got a particular expensive brand of air freshener hidden somewhere, and that if I didn't pay for it she'd have to stop me from leaving the shop. At this point I knew for certain that she'd made a mistake as I hadn't even been on the aisle where they would be. But I was in tears at this point, the queue behind me was enormous and everyone was watching. So I took off my coat, unzipped DS's coat and asked if that was proof enough as I definitely had nothing to hide. She sneered at me and said that she knew I had it somewhere but had got away with it this time. I asked her to clarify if I was free to leave but she went in the back room and ignored me.
I was so scared leaving the shop as I thought I'd be stopped, and was in floods of tears at this point. Had to drive out right away or risk getting a parking fine too! When I got home, (now-ex) DP called the store and spoke to the manager. He checked the store CCTV, discovered that yes, a mistake had been made, and put the security guard on the phone to apologise. She explained that carrying a babe-in-arms was a "common tactic" for shoplifters!!! But couldn't explain why she thought I had stolen that very particular item. I'd guess mistaken identity, but AFAIK there was no-one else in the shop carrying a young child!
I have never set foot in any of this chain's shops since then.
The public humiliation and shaming was the worst of it for me. Despite having received an apology both times, there would be no way to tell every single person who saw the incidents that the security guard had been mistaken, that I was not a thief!