The Shopping Reform and Modernization Act, or Scanner Law, requires that most items on store shelves be clearly displayed with the price; by signage, electronic reader, price sticker, or any other method that clearly and reasonably conveys the price to a consumer in the store at the place where the item is located. If an automatic checkout system (scanner) charges you more than the displayed price of an item, and:
the transaction has been completed, and you have a receipt indicating the item purchased and the price charged for it; Then:
You must notify the seller that you were overcharged, within 30 days of the transaction, either in person or in writing. Within two days of receiving your notice, the seller may choose to refund you the difference between the amount charged and the price displayed plus a "bonus" of ten times the difference, with a minimum of $1.00 and a maximum of $5.00. If the seller does not pay you both the refund and the bonus, you may bring a lawsuit to recover your actual damages or $250.00, whichever is greater, plus reasonable attorney fees up to $300.00. You may instead file a complaint in a small claims court without an attorney.
https://www.michigan.gov/ag/consumer-protection/consumer-ale...