Sly cashiers

I have to complain about some of Dis-chem Clearwater's cashiers. On Sunday 11th September 2022 we got home and for a second time found a tube of "Lifestyle Vitamin B fizz" in our bag and we paid for it although we did not put it down on the counter. Today my wife went into Dis-chem again and this time the cashier asked her if she wanted to buy a tube as it is on special. Do they get commission on the sale of this product? Is that why they scan it and put it into the bag on the sly? That is not acceptable though!!