Walmart
Cheating customers by charging me the wrong price and duplicate the charge on the same item

I purchased a multi-pack Pringles priced at 2.50 at the shelf. At the check, the scanner showed 2.98 per pack. I told the cashier that I was over-charged. He went back to the shelf and checked the price and agreed with me. I asked for the free product, he said Walmart does not have such a policy to give it out for free.
I am wondering is there any kind of law to protect the consumers to ensure the merchant is honest with the price charged at the check out? People do not remember or pay attention to the details in terms of what is the price at the shelf or what is the actual charges at the check out scanner. If the merchant is left to make "mistakes" and not not need to deal with any penalties for the mistakes, what is the incentive for them to ensure the check-out price is accurately reflective of the shelf price?

Company: Walmart
Country: USA
State: Pennsylvania
City: Kennett Square
Address: Baltimore Pike

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