It's been 10years since I worked for NCR, a business machine. ATM and cash register mfg.. I put 35 years in the company. Part of my job the last few years was installing self checkouts in major grocery store chains. Any customer over 40 hated them. I see the same problems plague the machines, namely any item that needs to be weighed, store employees assigned to watch the machines and assist customers are not patient enough to take the time to train customers on how to use the machines, any item erroneously scanned by a customer means flagging down a store employee to void the item and myriad more issues as mentioned in this thread.
I've read recently that stores like Walmart, Costco and even smaller stores are rethinking and de installing self checks because in store theft (shrink) and general customer dissatisfaction is growing. An example is if you key in code 4011
(bananas) and weigh a steak the machine doesn't know the difference between the two. I've seen store security monitor a check out lane. There's a camera watching what's scanned by a customer, and a duplicate receipt prints out for security. The receipt printed for security should match the items in the customers possession. Hiring additional security staff defeats the original purpose of the self checks, namely reducing the number of human employees.