RANCHO CUCAMONGA (CBSLA.com) — Crooks in Rancho Cucamonga are paying for Girl Scout cookies with counterfeit cash.

Two high school sophomores, Katelyn and Tari, were selling cookies Saturday in front of a Stater Brothers when they took in two seemingly legitimate $50 bills from a man and a woman.

READ MORE: Bystander Struck By Bullet In Downtown LA Shooting On Tuesday

When they tried to break one of the $50 bills, a cashier told them the cash was fake.

Troop leader Cheryl Williams was stunned.

“Even though we had the…counterfeit pen, the pen did not work. It showed that it was a good bill,” she said.

Also on Saturday, a mother at another cookie booth at a Vons in Rancho Cucamonga was given two phony $50 bills.

READ MORE: Santa Ana Winds Set To Return On Thursday

“It’s just unfortunate because our girls are trying to trust people,” the woman, who wanted to remain nameless, said.

On Monday, Teresa McMahon, a spokesperson with the San Bernardino County Sheriff’s Department, held a lesson on how to spot fake cash for the Girl Scout troops.

Parents were also given a handout.

“The difference is that if you look at the faces, they’re all the same here, and here you can actually tell by the shapes of their faces that they’re completely different,” McMahon said.

The Girl Scouts are chalking up this weekend’s event as a life lesson in funny money.

MORE NEWS: Man Robbed In Sherman Oaks After Fender Bender

“When you do put yourself out there, you are always going to have to double check,” Tari said.