A friend was shopping in a small DIY store carrying his toddler in his arms and over his shoulder....
When he arrived home and took off his big, furry anorak he found that his little one had filled the hood with small packets taken from the shelves she could reach as he walked around......nails, screws, washers etc......yes, he went back... :-)
In my case the cashier would not be affected if i didn't inform them because no one would have been the wiser .
Also , given that the SM is one of the big 4 , i doubt that one item being missed would have registered anywhere in their system ; given also the item of food was a 'create your own'
In the dim distant past when using a cashier I have noticed an error and pointed out the missed item. Have also found things when I got home, nothing of any value but couldnt be bothered, my time is money too after all. I probably would if it was of significant value, but then that sort of item probably doesnt get mistakes.
Funny enough a similar thing happened just the other day at Tesco... I was nattering to the lady at the check-out (Old woman that I am) and she asked an Item back as she hadn't scanned it, I was more than happy to do so.
I went back to a pub to pay for a pub meal bill - but everyone knew my Dad so it wouldnt be forgotten but more discussed if I didnt ( gor social pressure in Darzet!)
and to a chinese to pay for the lobster ( 'we want to come back here!') -
oh and at a garage which sold xampagne ( excuse me was that champagne?) - I said you havent charged me for 5 bottles - and they said no we charged charlie the one before you. yeah £200 for a can of petrol and he didnt notice ....
and it was quickly sorted....
£3.60 hmmm - oh did I tell you that the grooms half sister did a runner from his wedding ( that must be wrong !) and so they plooped her room charge on MY bill which I paid in a haze - - - and then .....
everyone wondered why I didnt pay Saucy Salz charge without comment, instead of squawking like a girlie.
I got to my car with my trolley, and groceries in bags. There were a couple of items in the bottom of the trolley that might not have gone to the cashier's shelf, or might have fallen out of the bag after I'd paid. The cashier had thrown away my receipt, so I couldn't check. I just kept them.
Every time I go to that supermarket now I double check that everything's gone through.
I have more than once been charged for two items after purchasing only one. Never bothered going back as I would have to lug all the shopping to be compared to receipt etc. Have occasional item not ringed up for, ditto. Swings and roundabouts.