I think there are five main issues with auto-checkouts - each with its own particular cause.
Issue 1 The machine doesn't make smart decisions, or let me short cut its workflows - e.g. if I've entered a debit card, I automatically want to pay by card, but the machine insists I remove the card, press 'pay by card' and try again.
Possible cause? Designers who take for granted the workflow the supermarket imagines users will take rather than practical insights into the ways shoppers actually work. Lack of attention to the 'NATty principle' ('Never Ask Twice').
Issue 2 Autocheckouts rely too much on human supervisors arbitrating decisions, when assistants are usually in short supply and often busy directing customers to terminals.
Possible cause? Miscommunication about the context of the product. I strongly suspect that whereas the designers were assured that supervisors would always be on hand to help, supermarkets have 'sold' the service internally as a way to reduce supervisor workload. That would mean staffing managers under-resourcing autocheckout lanes, yet designers assuming a supervisor will always be able to help.
Issue 3 Poor item detection. Too many items get flagged as 'invalid', and I have to get a supervisor to help.
Possible cause? Probably just limitations in item detection combined with excessive concerns about shoplifting and malicious users. Misunderstanding that failures make a serious impact in this context, because assistants are not always readily at hand.
Issue 4 Intolerant timeouts - if I'm having trouble bagging something, and I take a little too long, the entire terminal closes down, and I can't continue - even if I do eventually bag the item in question.
Possible cause? This could be simply a lack of practical research, combined with hasty assumptions about how long something 'should take' - when research will indicate something very different.
Issue 5 Cannot rebag items; performs poorly when I have multiple bags.
Possible cause? Hasty assumptions that I would never remove an item from a bag after I'd bagged it, and that I'd always have one small basket - in other words, assumptions that I'd work to the workflow the designer or supermarket imagines is likely, not what actually happens in practice. Inability to accept alternative workflows.
How could the designers have done better?
- better thinking about the pragmatics of deployment, and not assuming the availability certain resources (supervisors to assist; maintenance to keep touchscreens clean and thus responsive)
- field research into how undirected shoppers will actually proceed; healthy scepticism about assumptions regarding workflows and behaviour
- better handling of failures in workflows; better research into impact of 'lockdowns'