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Comment by SubiculumCode | Hacker News Reader

This is what I think about at the pump.

More and more I see gas pumps ask if you want a receipt BEFORE the gas is dispensed. This seems risky.

If you decline the receipt and then dispense gas, the pump could cheat on the amount of gas dispensed with less risk, as a papered record of the purchase amount and price is not produced.

If on the other hand, the pump waits to ask if you desire a receipt until after the gasoline is dispensed, the dispenser will not know if a written record will be requested, and cheating the customer is riskier.

Therefore, I always request a receipt if asked prior to dispensing my gasoline.

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Maybe related, we had an event in my small town where a customer pressed diesel, but got filled with regular unleaded. His receipt helped him when fighting for some damages.

Certainly having the receipt doesn't actually do anything? Do you measure the volume of gas in your tank before and after filling up?

Regardless, this seems very easy to test. Just fill up a gas can and check that you're paying the right amount for the amount of gas in the can.

Without a receipt there are two things that can be a problem: 1) Less gas is pumped, 2) Charged more than the pump said.

True the receipt protects against 2) more than 1) because the car's tank does not have an accurate guage.

I remember listening to a story once about a fraud at the gas tank in which the normal amount of gas was only given out when requested in an even increment a five gallons which was how much The Regulators requested when they came and tested a gas stations pumps. they were caught after a spicious regulator requested an odd amount of gasoline and got the wrong amount.

with a combination of receipts and camera/ML classification that classifies when a customer is filling a tank versus filling their car will allow avoidance of weights and measures regulators. This is a problem I foresee.

Gas is common enough and such a hot button issue that mass fraud like that would be easily noticed on credit card statements and in the tank. It's easy to test, confirm and verify, and can be done by just about anyone. Pull up to the station, fill up your gas canister, and check the price, volume etc.

The places where this fraud is most likely to exist are niche markets and places where it's hard to verify. Walled gardens of software or hardware with few outputs to measure.

On the other hand, there's a reason why the pumps have those weights and measures stickers on them.

Car manufacturers could also install more precise sensors in the gas tank and report the amount of received gas.

But they could collude... o_0

The hard part with that is, see the sticker on the outside of the pump? That certifies that this pump meets your state's regulations and that someone has inspected it recently. In order to have a coverup like that, you'd need the government to be in on it too.

http://articles.latimes.com/1998/oct/09/business/fi-30669

See link for a scam using an altered microchip and scheme to protect itself from discovery by weights and measures.

You mean like the EPA sticker on a new Volvo?

I don't know about that - all that proves is that the pump hasn't been opened since inspected. While I suspect even that isn't foolproof, there's nothing stopping someone from modifying the pump through external means, whether through a remote firmware update or mechanical means, like a magnet placed on the outside of the pump that engages some hidden mechanism.

Wasn't the danger of encountering devices (somehow) programmed to act differently in a regulator's test regime than in daily use one of the points made in the article? (Actually achieving this in the gas pump situation is left as an exercise to the reader.)

What sort of weird gas station requires you to specify the amount of gas before actually refueling your car? Is that a USA-only thing? Never seen that in Europe.

I don't think OP was saying that. The pump asks Y/N if you want a receipt before you pump, but prints it after the pumping.

That said, you do specify the amount of gas if you're paying cash here in the US. You go inside, say "here's $20", and the pump will dispense exactly that.

If you're paying with cash you usually have to prepay. If you're paying with card the station does a preauth on your card (and usually a temporary hold) then does the final authorization after you finish pumping and it knows the total. Sometimes you have to pump twice if you want to go over the preauth hold amount, which is usually $50.

It's worth noting that it wasn't that way the entire time I was growing up. You would pump first then pay the cashier. It wasn't until around 2005ish that I noticed signs instructing cash customers to prepay.

Also in Italy, if you pay cash at the pump you have to specify the exact amount. And woe to you if you over estimated how much you'll need < there's no change.

It's not required, but, in most self-serve stations I'm familiar with (Costco being the exception), you can prepay with cash (e.g. ask the attendant for $20 on pump 5, or whatever), and the pump can be set to stop after $20 worth is dispensed. If less than $20 in gas fills your tank, you can get change from the attendant. This is commonly done late at night or for pumps not visible from the attendant's vantage point, to prevent drive-offs.

I've seen it in Norway, Italy, and somewhere else before. It's not terribly common—or it's usually optional and most people don't realise you can do it.

Having just done this particular drive, it's all over Iceland.

This is common in Iceland as most pumps let you pay with card at the pump so you pre-auth from a number of options and get charged the actual amount you pump.

In Portugal this is common on SelfService stations as well. To avoid the obvious "fill-up and drive away" style theft.

I think they are using the receipt prompt to hide how long credit card authentication is taking.

They can't easily cheat on prices as usually there are large signs displaying the current price. They can't easily be cheating on amount dispensed, as the pumps are regularly checked by the local Weights and Measures Department (doesn't rule out a VW like cheat though).

Yeah. Inspectors use a 5-gallon container to test gas pumps:

https://www.youtube.com/watch?v=m9HG_3SIsEM

So, your gas pump has to be accurate for the first five gallons, but then you can cheat as much as you want.

The only saving grace is that the people who make the pumps and software wouldn't be the main benefiters from cheating at the pump. So probably we're actually okay for gas pumps. It's situations where the software creator also benefits from the sales using that software...

But maybe I'm wrong. Maybe independent gas station operators are buying bootleg software ROMs to flash their pumps... "Boost revenue by 10% with this one easy trick"

And, I see from another comment:

http://articles.latimes.com/1998/oct/09/business/fi-30669

As much as I am confident many pump operators out there would do anything to make a quick buck at the customer's expense, all it takes is one time metering more gas into your tank than what your tank is able to hold, after which you know they're lying and regulators will get involved. Even if not, word of that kind of thing spreads and it won't be long before that filling station's competition starts stealing its business through word-of-mouth.

Pair that with cameras to classify whether it is being pumped into a car or into a portable tank.....eesh

Where do you live that you can get a receipt? The printers never have any paper in my area.

Can't you report them if they never have paper?

I've seen "out of paper, cashier has receipt" before. Never seen "out of paper, too bad, no receipt for you" before.

But according to this theory, it sounds as if one should ask for the receipt afterwards?

By one do you mean the consumer? Gas pump software seems to come with two variants: 1) Ask before pumping gas. 2) Ask after pumping gas.

I see the misunderstanding. You're thinking that the pumps should be designed to always give the receipt afterward. Yes, that would be the ideal way to reduce the possibility of cheating.

However, in the pumps he's talking about, the machine prompts you beforehand: "Click here for a receipt". The receipt decision (yes or no) is always before. There is no way to ask for a receipt afterwards.

He always asks for a receipt (even if he doesn't need the receipt) because he figures that the machine is less likely to cheat him in that case.

One can always get a receipt from the attendant after the sale, at least at every gas station I have ever been to.

And then kill everyone involved in the project to prevent them from whistleblowing.

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