Well there was the TV that they lost after it blew up after 3 months. I had to hit them with moneyclaim after 6 months of getting nowhere with them.
Then there was the kids shoes I bought which fell to bits after a week (soles came off on both shoes) and when I returned them immediately they accused me of swapping them for another pair and refused to refund. They only actually did anything after I informed them that if they didn’t sort it I was going to spend the afternoon in their shoe department showing everyone the crap they sold.
Then there was the time I bought a toaster which caught fire and they said I was using it wrong (wtf). The entire model line had been recalled by the manufacturer which was published on their web site and they were shown that and still refused to do anything.
John Lewis are just total shysters leveraging a reputation they created through marketing.