20% seems like a "significant portion" to me

20% is an incredibly high number though, if a store has 400 people/hour that means you're manually reviewing 80 transactions per hour, over one transaction per minute. That's multiple human employees.

One transaction per minute is nothing at all when the transaction can be as simple as "did the person put that back on the shelf" with a 5 seconds clip.

Proven "false." I've noticed that if one admits the truth with a dismissive or offended tone, you can just continue to claim the lie and through sheer force of will people will still go with it.

I think people just think that they must be misunderstanding something; that nobody could claim one thing while offering evidence of its opposite. 1/5 of purchases lose their significance.