The store robbing the customer is colloquial language, as robbing is the act of taking something without permission (and I assume he gave full consent when handing over his money, though he was overcharged). The second question doesn't really make sense. It should be the future tense and therefore "If the store robs the person, he'll (he will) report it to the police".
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Guyper1."The store robbed the person by overcharging him"
2."If the store robs the person, he's report it to the police"
Thank you