HOUSTON -

You're asking Amy about overcharges at the checkout, and she knows a little something about the subject.

She just wrapped up a year-long project we've dubbed "Operation Price Check." Investigator Amy Davis explains how much she was overcharged in 12 months, how she got the grocery store to pay for its mistakes and how you can do the same.

It all started when Davis was overcharged at her grocery store several visits in a row, and it ended with a decent little windfall for a deserving Houston charity.

The allure of a sales tag promising a 20-cent savings will work every time on a bargain shopper, but what if none of the shoppers who bite see that 20-cent savings?

It happened to Davis, and after a series of overcharges at her local grocery store, she wondered how much she was losing every year because of pricing errors.

Do you even stop to check your receipt?

"I always watch my receipts," shopper Mary Robinson said.

"I don't usually check it at the store, but I always check it at home," shopper Jennifer Lee said.

"I do look for the discounts," shopper Norina Silva told Davis.

For a full year, Davis checked her receipt every single time a cashier checked her out, and then she called them on every overcharge.

Sometimes she shopped with a hidden camera, and out of a total of 90 trips to the Kroger on 11th Street near Shepherd Drive in the Heights, she was overcharged on 23 trips. That means 25 percent of the time she shopped at the store, she was overcharged. She overpaid a total of $60.99. 

"At times, did errors occur? Absolutely," Kroger spokeswoman Rebecca King asked, then answered her own question.

KPRC Local 2 gave Kroger a copy of every receipt with an overcharge so the store could do its own research.

"We feel that a good way, an accurate way to base this study is based on the number of items that you actually purchased," King said.  "So the researcher purchased about 1,057 items specifically. We felt that there was a potential for error on about 26 of those items, which is an error rate of about 2 percent."

King said in some cases she thinks Davis may have picked up the wrong item or perhaps a sale sign stayed up long after a sale was over.

"In some cases, it's just really hard to tell," King said.

Still, at the end of the year, instead of getting short-changed, Davis came out ahead, and so did the Houston Food Bank.

"We found $145 that we wanted to donate to the Houston Food Bank," Davis told food bank president Brian Greene.

"Oh, well, thank you very much," said Greene. "How did you find the money?"

Good question. Kroger's "scan right guarantee" promises that if any item you purchase scans incorrectly at the register, you get one of that item for free, up to $25.

For example, Tropicana orange juice was on sale for $2.50. At the register, Davis was charged $2.88. According to Kroger's "scan right guarantee," she gets a refund of not just the 38 cents she was overcharged, but the full price of the product, $2.88.

Our $60.99 in overcharges turned into a refund of $142.61. We rounded up and gave the Houston Food Bank $145.

"This money is very much appreciated," said Greene. "We're going to get a great multiplier out of it and a lot of food is going to go out."

When we told you about "Operation Price Check" in July, a lot of KPRC Local 2 viewers e-mailed Davis and said they have a hard time getting the cashier to honor the store policy and give them a full refund on the entire price of the product.