I remember watching one of thevUndercover Boss type programmes on tv years ago (Back to the fłoor?) where the head of one of the big supermarkets went back to working in a couple of their shops.
This was maybe 25-35 years ago when there were lots of deep trolleys and handbaskets, very few of the shallow ones.
He was shocked by the number of customers who wanted a shallow trolley but when there weren’t any, took a hand basket instead. Their conventional reasoning was that they would take a deep trolley instead and thus be more likely to forget how much they had picked up and thus buy more, resulting in more profit. That people would pick up a hand basket just hadn’t entered their minds and seemed completely illogical to them.
The guy realised that their shortsightedness and determination to foist bigger trolleys in customers was actually backfiring and losing them sales as they were only buying a hand basket of stuff instead of a shallow trolly-load.
One of his first actions even while he was still there undercover was to ring up and order a load of shallow trolleys and get a decent study going to see if what he was seeing was true across the rest of their shops.
In the summing up bit at the end, turned out it was true and hence they (and most of the other chains) switched to having about half and half deep and shallow trolleys.
Thinking they should do that study again as they always run out of shallow trolleys first and you hear people complaining they have to have a deep trolley!