For your self checkout point I'm convinced they're configured differently based on location, I hated using self checkout in the 'bad' Walmart I used to live by because it'd constantly complain or summon the attendant if I scanned stuff too fast or if there was a tiny weight discrepancy, but when I would go to the 'good' Walmart I had zero issues.
2.9C is still really bad though, so I'm not sure what you're trying to say.