If there is a discrepancy between the price listed on the shelf or item and the price that it rings up at, the consumer must be offered one of two corrections:
If the item costs more than $10 and rings up higher than the advertised price, $10 must be deducted from the price.
If the item costs less than $10 and rings up higher than the advertised price the item should be given as free.
So, David was making a big stink and probably has the law wrong. Also, it is for "food and grocery" stores. Not sure if a toothbrush would count, but I'm not gonna look that up.