[dave78]

I wonder if there are larger implications to reverse-engineering this. When I worked in retail in high school, I was told repeatedly that if a price was marked on a shelf, then there are laws that require the store to sell that item for that marked price. (IANAL so I don't know the nuances there, but it makes sense). If it becomes easy to change these displays with a new price wirelessly, that could be a really nasty problem for any stores using these displays.

Hopefully for the store's sake, there'd be some sort of public/private key system so that only the holder of the private key can distribute price changes wirelessly. I wouldn't bet money on that though.

(edit) - I see someone else posted the manual and that there's a per-site AES key. That's a good sign I guess.

[dcow]

I’ve only seen a store honor the floor price when it was clearly wrong like once and it was for an item that they were trying to get rid of anyway. I’ve heard the lore too and can’t understand how it could be legally binding for a store to sell an item at the sticker price. Wouldn’t people just walk in with little stickers and mark stuff down as they wished? My wife works in retail and confirms that stores don't just give out items at a loss when the price is mislabeled. They fix it and apologize. My experience confirms this too.

These days stores essentially just map an item’s UPC to a price in a DB in their point of sales software. The price isn’t encoded on the tag. Which brings me to my question: why the heck are we making an eink price tag with heavy security when the source of truth is the POS anyway? I mean no negativity about reversing one, it’s a super interesting and fun project. Just, “why?” in the first place does this thing exist? Maybe it’s just convenience and saves on labor costs to be able to update the price of all the items in your store at once and not pay a human to go out and relabel them?

[rhd]

Here's an example in Michigan's law:

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...

[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.

[reaperducer]

the source of truth is the POS anyway

In a technical, ideal sense the PoS is the source of truth. But life is messy.

PoS may lose connectivity. PoS may be running an outdated version of the software. PoS is based on some unreliable operating system or low-end PC, and is unreliable. PoS doesn't know about the store manager's last minute special because the distributor sent too much stock. Stores don't have in-house IT guys.

From a legal standpoint, in some states, the price on the shelf label is the source of truth. My grandmother lived in a state where if the price on the shelf was lower than in the PoS you got the item for free.

She was very good at catching those errors and complained bitterly when the law was changed so that the customer only got the lower price.

[bsder]

> I’ve only seen a store honor the floor price when it was clearly wrong like once and it was for an item that they were trying to get rid of anyway.

I bought six packs of Diet Coke from Target at a discounted price for almost 6 months because they left an old tag up at one particular store. :)

[mig39]

I once scored a big bunch of coffee because the local Canadian Superstore confused cents with dollars. The price was listed in cents per kg instead of dollars!

At first they refused to honour the price, and fixed their mistake.

I sent an e-mail with photos to their corporate office. I received a phone call from someone who was laughing and thought it was all funny. He told me to go back to the store, and as much as I could carry, they would honour the posted price.

Cost me like less than a dollar for 4 or 5 kilos of coffee!

[kwhitefoot]

That's a heart warming story! That head office was amused and honoured the posted price. They would probably have been within their rights to refuse to sell. At least that is the way it works in English law. The price label, etc., is 'an invitation to treat'. That is it is an invitation to enter into a contract, not a contract in itself. Unless it's changed since my wife studied the subject in the 70s.

[ThePowerOfFuet]

Loblaw can definitely afford it.

[adversaryIdiot]

That is awesome to hear