If the price for milk has changed and they failed to update the sticker on the shelf, the cashier might be unable to sell you milk for $1 if the register system

If the price for milk has changed and they failed to update the sticker on the shelf, the cashier might be unable to sell you milk for $1 if the register system says $2: you can either pay $2 or go home without the milk. (While there might be a law that a sticker price must be honored, the cashier might not know how to override the system.) This is mostly to say that even in a milk-price situation, you'll want to decide on the circumstances and how much is milk urgent for you. OTOH, can you imagine a (non-trivial) contracting job where there was not a single change in requirements along the way?