SAN DIEGO -- Americans spend an estimated $25 billion a year on gift cards, and now scam artists are using them in an elaborate new scheme to take advantage of San Diegans.

Sue Grant's dad experienced problems using two $100 Visa gift cards she had given him.

"When he went to use them at a gas station, they both were both declined," said Grant.

When she took a look at the cards she noticed something very suspicious.

"You pull the card out and there's this fake bar code on top of the real one. So when they scanned it, they scanned the fake barcode. They didn't scan the real card," said Grant.

In a similar scam, a bogus barcode is actually sealed to the window of the packaging and not the gift card. The only one cashing out on these cards are the thieves diverting the funds.

Grant bought the gift cards at a Ralphs supermarket, and it's believed those behind the scam steal stacks of gift cards, doctor them up somewhere else and then slip them back into the store for unsuspecting consumers to buy.

"I'm amazed at this scam, because it is so elaborate and because they've apparently gotten so many people so quickly," said Sheryl Bilbrey of the Better Business Bureau.

Bilbrey said there is no limit to how far scam artists will go.

"Once the card is scanned, you get a tape from the grocer or retailer that shows the number on the back of the card. So those two numbers should match as well. I would check those before you leave the retailer's facility," said Bilbrey.

Grant said, "I have the authorization receipts. The numbers don't match the card number."

Because Grant had her receipts for the gift cards, she was able to get reimbursed.

10News received calls from other victims who said they also bought bogus gift cards at a variety of retailers.

A representative for the Ralphs store where Grant bought her gift cards told 10News they are working with San Diego police and their own investigators to try and catch the scam artists.