I have never once used that prompt to catch or respond to an error. It gives so little actionable information. That's what watching the display that totals up your scanned purchases is for. Sure, I guess some people might use that screen as their method for catching an error, but it should be caught before you're given a number and asked if its correct.

Why I think that screen is there is to shield a merchant from someone coming back after the purchase to complain. And I doubt any merchant would use that confirmation to defend an error and risk losing a customer. Which, to me, makes it even more useless.