A pair of counterfeiters took petty crime to a new low when they used fake money to buy Girl Scout cookies. Even worse, they reportedly got change in real cash after paying with fake $50 bills, leaving the girls stuck with the bill.

"The girls are heartbroken," Rancho Cucamonga, Calif., troop leader Cheryl Williams told ABC affiliate KABC. "Because they do trust, this is a life lesson for them."

At least two thieves used the counterfeit money scam over the weekend, setting the Girl Scouts back about $200.

“We are appalled that anyone would use counterfeit money to steal from a Girl Scout. This crime takes away proceeds from Girl Scout Cookie sales that fund girl programs and projects in our community," Girl Scouts of Los Angeles spokesperson Carol Deitrich told Yahoo News on Tuesday. "Obviously, the girls are not experts at detecting counterfeit money. So, even though we have safety precautions in place, this sort of thing can happen."

Williams says the girls took all the necessary precautions. They "used the counterfeit pen on the money, and it worked," Williams told the station.

The fraudulent $50 bills were used at two different locations in Rancho Cucamonga over the weekend. In each case, the girls went into a grocery store to make change and were told the bills were fake.

In May 2013, Girl Scouts in Oregon were victims of fraud when someone falsely tried to order $24,000 worth of cookies online through a fake company. In that case, local residents chipped in, buying thousands of boxes of the cookies to help offset the costs incurred by the troop.

Police officials say they are reviewing surveillance video outside the grocery stores where the Rancho Cucamonga sales took place. In the meantime, they have issued instructions to the Girl Scouts on how to spot a fraud: Turns out it's all in the faces that appear on the counterfeit bills.

“The difference is that if you look at the faces ... you can actually tell by the shapes of their faces that they’re completely different” from real bills, San Bernardino County Sheriff’s Department spokesperson Teresa McMahon told CBS Los Angeles.

Yahoo News contacted the greater Los Angeles branch of Girl Scouts of the USA to see whether counterfeit scams are an ongoing problem and whether there is any recourse for the girls, but has not had a response.

Still, becoming counterfeit bill experts might be a tall order for teens and preteens who are more focused on trying to raise money for their organization.