Even if you balance the double charging with a chance to get an item for free (or negative price, acting as a credit), humans will still complain when they get

Even if you balance the double charging with a chance to get an item for free (or negative price, acting as a credit), humans will still complain when they get double charged and stay silent when they get the bonus. But of course there's rich people who don't even care they were double charged for something like groceries. Most of these issues aren't about how many 9's of reliability there are, but whether or not some person is accountable. AI is not itself accountable, only the person in charge of it. Many companies already give gift cards or whatever when a human mistake happens as a form of customer service, and there's not enough compensation around AI error rates to make them palatable.