MADISON, Wis. -- With back to school shopping in full swing, Wisconsin stores are slashing prices hoping to lure customers.

But there may be a difference between what shoppers think they're paying, and the price they actually pay. By state law, customers are supposed to get refunded any overcharge.

Hoping the avoid pricing mistakes, the Wisconsin Department of Agriculture, Trade and Consumer Protection is putting many local stores to the test.

As the McFarland mother, shopper Elizabeth Fritz said she does some last-minute, back to school shopping for her sixth-grader

"I'm trying to organize an 11-year-old if that's possible," said Fritz.

Meanwhile, another parent is hitting the aisles too, but Jared Williams isn't checking off a list. He's looking for pricing mistakes.

"An error is either an overcharged or undercharge," said Williams. "We do count either one as an error."

Williams, a weight and measures inspector for DATCP, said he inspects grocery and big box stores like Shopko once a year.

"Errors happen. That's why they're allowed a 2% fail rate so they're allowed one item out of 50 scanned," he said.

Penalties for two or more errors range from additional information to fines. Last year, seven stores in Wisconsin had to pay $250,000 in fines as a result of weights and measures price scanner inspections.

"Yes, I have seen stores that have had large percentage errors," said Williams.

Once finished, Williams prints off barcodes from 50 randomly selected items and heads for the register.

"It's the responsibility of the store to make sure their prices are accurate,” he said. "But everyone is human and there's eventually going to be errors. They might miss something."

Out of 50 items scanned, Williams finds one mistake in the pricing of an infant pacifier.

"So this is actually an undercharge which is a good thing," he said.

The price on the shelf is higher than what the customer would pay at the register. The error was later dropped when the store manager showed Williams a sign near the item advertising a 10 percent discount.

While this store passed with flying colors, state officials said that it's also up to shoppers like Fritz to do their part.

"I pay attention to when they're scanning to know what's going through is actually what I was charged," said Fritz.

DATCP officials advise customers to bring the store ads with them, write down the prices as they shop, watch the display screen as items are being scanned, speak up if they think they are overcharged and demand any refund while they’re in the store. They may also want to look for the store’s pricing error policy.

DATCP also suggests consumers to report errors to state or local inspectors.