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Guru
You don't have nearly enough evidence to know if it's fraud or not. Nothing you witnessed is a prima facie crime. It requires information only the store would have to know it's fraud. So the police would tell you to do what you did : tell the store. Then if they see it as fraud and chose to press charges, they can bring it to the police.
*Your opinion
*How do you know what other evidence I do or don't have?
*Anything else you want to point out with points?