I believe Michigan has laws on the books that should be the model for this (the "Scanner law") - if you're overcharged at the register and the sale is completed, you have 30 days to get the price corrected plus ten times the amount of overcharge (between $1 and $5). Paying you the 'bonus' is optional, but if they don't do so you can file a suit for the greater of your actual damages or $250 (in small claims on your own or regular court which allows up to $300 in attorney fees).

An alternative would be to force stores with mischarge rates exceeding a specified level to close until they've completed a full audit of all shelf prices in the store but in some areas that could cause significant local hardship.

> force stores with mischarge rates exceeding a specified level to close

They'd leverage it as if it was an allowance and stay just below that rate.

That is already ludicuously complex. Designed by Kafka so you give up.