Dave, I used to work in a supermarket and that did happen.
There were also the people with cardboard grocery boxes in the trolley with false bottoms, which they filled with food and then emptied onto the checkout belt, except that the expensive steaks remained hidden in the boxes.
And the ones who ate food while they went round the shop, and then hid the wrappers somewhere on the shelves.
And the regular customers we needed to help unloading their trolleys, not forgetting the large pack of washing powder under the trolley on the wheel arches ("Oh, I didn't realise it was there - this is my sister's trolley").