A penalty for overcharging customers at one of Auckland's biggest supermarkets, Pak'nSave Mangere

In June and October 2018 -- mystery shoppers found the store was charging more at the checkout than the price advertised.

On four occasions, sliced salmon was displayed at eight dollars 99 but charged at ten dollars 79.

Commerce Commission Chair Anna Rawlings says the discrepancies may seem small, but that doesn't excuse the supermarket.

She says all consumers are entitled to pay the price represented to them -- and that they expect to pay.

The supermarket must pay an almost 80 thousand dollar fine.