It's incorrect to assume that a customer should be happy being compensated for minutes at the same hourly wage the store would have paid a dedicated cashier over the course of a whole day. Rather for on-demand piecemeal work done by a more skilled generalist, a much higher rate is appropriate. In addition to a minimum call out time, of course.

Personally I just avoid self checkout unless I only have one or two items and the lines are bad. But even then it's not often worth getting annoyed by the sluggish hyperprescriptive workflows.