SEATTLE -- Most businesses use scanners to ring up a price. In Seattle, it's the city's job to make sure the scanners are more than 98 percent accurate.

If a business fails a city inspection, they get a warning. Do it three times in a row and the business owner could go to jail.

Let's be honest. When it comes to checking receipts, how often do you really pay attention?

"I rarely check because, who has the time?" said one consumer.

Another shopper said they checked their receipts at least half the time.

So many products -- so many bar codes. It's becoming harder and harder for consumers to track what they buy.

Craig Leisy with the city of Seattle makes sure that consumers don't get overcharged. He oversees price inspections for about 450 Seattle stores.

"We save millions of dollars for consumers a nickel at a time," said Leisy. "We try and get around to every store each year. These are unannounced inspections."

Most pass, but some do not. Our investigation found several businesses that were overcharging their customers.

Records show that a Shell convenience store, owned by ARS West on 511 South Dearborn Street, failed three consecutive price check inspections in 2006.

So did another Shell store on 700 12th Avenue.

"We put a store on an accelerated inspection schedule if they fail. Instead of doing an annual inspection, we will do one every three months, and that seems to do the trick," said Leisy.

But not for ARS West. Since two of their stores failed three consecutive inspections, the city filed criminal charges.

According to inspection reports, all nine of ARS West Shell stores failed at least one price inspection between 2006 and 2007. Seven stores failed two consecutive inspections while two others had three successive overcharge violations.

In an e-mail to ARS West from the city of Seattle, inspectors call the violations the worst they've ever seen. One store had 13 errors out of 25 items checked. Eleven of them were overcharges.

ARS West district manager Jerry Lawrence agreed to talk with us on camera. He admitted there were problems.

"It's not the right way to run a business so we want to make sure it's accurate," said Lawrence.

"It seems more than an oversight," said KIRO 7 Consumer Investigator David Quinlan.

"Well, it's difficult to say. We've made some mistakes. There were some undercharges that were prevalent, but the city doesn't recognize that in their inspections," said Lawrence.

"Undercharges are sometimes are important as overcharges. They indicate that the store does not do a good job managing pricing accuracy," said Leisy.

ARS West reached a settlement with the city of Seattle. The store manager said the mistakes have been corrected.

"The system was as effective as it needed to be and we made those changes," said Lawrence.

Other stores that had trouble were Joe's Incorporated on 328 Northgate Way. It failed three consecutive price inspections.

Seven other businesses failed two successive inspections between 2006 and 2007:

Office Depot - 1423 Fourth Avenue and 4900 25th Avenue Northeast

Ballard Market - 1400 Northwest 56th Street

Kaufer Company - 901 Harrison Street

Morgan Electric & Plumbing - 3627 Stone Way North

Paper Zone LLC - 1911 First Avenue South

Pete's Supermarket - 58 East Lynn Street

Radio Shack - 3820 Rainier Avenue South

"We're not trying to be punitive. We want people to be in compliance," said Leisy.

And most businesses are. In fact, city inspectors say they see more undercharges than overcharges.

"It's pretty important. I've taken things back to the store to make sure I got the right price," said a shopper.

As for consumers, experts say they need to do their own policing as well. Check receipts, and don't be afraid to ask for a price adjustment even if it's only a dime or two.

"It contributes to the price of a coffee or tea," a shopper pointed out.

Keep in mind that the city tries to work with businesses if they fail a price inspection. If a business fails three or more consecutive price inspections, the owner faces a criminal misdemeanor charge.

ARS West, who runs the Shell convenience stores, said they are working with the city. The district manager tells us their stores passed all inspections over the past six months.