Aren't all these transactions checked by a human after the fact? IIRC I interviewed someone who worked on this and thats what they said.
Amazon had used roughly 1,000 humans in India, according to some news reports, to help monitor accurate checkouts. The company told CNN it’s “reducing the number of human reviews” while developing the “Just Walk Out” technology. Amazon said besides data associates’ main role in working on the underlying technology, they also “validate a small minority” of shopping visits.