This happened to me this week.
I looked at my register tape as I was leaving a grocery store. At the top of the list was an item that I knew was supposed to cost a little over $8.00.
The item was scanned and rang out at over $13.00. I went back into the store and explained the problem. An employee then went to the product aisle to check the listed price. After a few more minutes, I was given a refund for the overcharge.
This probably happens to other customers. Always double check what you are charged for scanned items.