[dave78]

I think that page backs up what I thought, at least for Michigan. The law views the price displayed on the shelf as being the correct price, and if the POS system doesn't match then the law says the POS system is wrong. Also there's another interesting FAQ there which further reinforces it.

Now, if an e-ink display is changed by a hacker, that's obviously fraud and presumably the store wouldn't have to pay up, but I assume that would be tough to catch because the store wouldn't likely assume it had been hacked and even if they thought so they'd probably have to prove it somehow.

From the FAQ:

What if the wrong price is displayed for an item and the clerk catches it before I pay; am I entitled to buy the item at the displayed price?

This is a fact-specific question best answered by a court. A store may not knowingly charge or attempt to charge a price higher than the price displayed for that item. Therefore, the consumer may have a claim if the store will not sell the item at the price displayed. However, the consumer may face obstacles convincing a court that the store knowingly charged the higher price when the pricing mistake is not intentional and will result in an obvious windfall to the consumer.

[dcow]

So the nuance is:

1) you’re only entitled to damages if the store actually completed the sale and the item rang up higher than listed on the shelf

and

2) the store is not required to honor labeling mistakes and can’t be compelled into a sale in that situation

This is consistent with my experience. So I guess if you’re trying to cheat, you don't tell them and ask them to adjust the price, instead you complete the sale then notify them of the error afterward. My experience has mostly been with notifying the employee beforehand which causes them to correct the labeling mistake if one was made.