A Guardian investigation reveals Dollar General and Family Dollar stores often fail to honor their shelf prices – charging more at checkout for everything from frying pans to Frosted Flakes

On a cloudy winter day, a state government inspector named Ryan Coffield walked into a Family Dollar store in Windsor, North Carolina, carrying a scanner gun and a laptop.

Inside the store, which sits along a three-lane road in a county of peanut growers and poultry workers, Coffield scanned 300 items and recorded their shelf prices. He carried the scanned bar codes to the cashier and watched as item after item rang up at a higher price.