I used a self-scan checkout in B&Q once to buy a tin of paint. The till charged me for a wheelbarrow, the machine made all sorts of Dalek-like noises, flashing red lights came on, I waited two or three minutes for an attendant to sort it out, she couldn't so I walked out leaving behind my paint (or was it a wheelbarrow?) I haven't used one since.
I've spent my working life using all sorts of modern machinery and electronic wizardry and I'm by no means a Luddite or a technophobe. But I am not going to ponce about scanning goods that I have had to find, load into a trolley, unload onto a belt, reload onto my trolley and cart to my car. It's not too much to ask of the store to provide a staff member to scan the goods for me whilst I pack them and any that don't do not deserve (or will be granted) my custom.