My experience is that self-checkout works extremely well until it... Doesn't. And then you need a human anyway. The "doesn't" only happens to me rarely.
But when something goes wrong it becomes immediately clear that---whether at a grocery store, convenience store, or anywhere else---almost no business deploying self-checkout has a real plan for handling the edge and corner cases where it fails, freezes up, or spits out an error.
Most stores that want self checkout to replace five to ten employees with just one to supervise but do not then make sure that the one employee can actually handle the self-checkout's failures and errors.
I had a relative who had a summer job at Ikea monitoring self-checkout:
1) the system and software were unfriendly to both users and staff, especially in error states, as you suggest
2) many people needed rudimentary help
3) no time to look for theft due to 1) and 2)
4) surprising number of couples arguing with each other
But when something goes wrong it becomes immediately clear that---whether at a grocery store, convenience store, or anywhere else---almost no business deploying self-checkout has a real plan for handling the edge and corner cases where it fails, freezes up, or spits out an error.
Most stores that want self checkout to replace five to ten employees with just one to supervise but do not then make sure that the one employee can actually handle the self-checkout's failures and errors.