> Real cardholders almost never buy something for exactly $1.00. Coffee is $4.73, gas is $52.81. The roundness is the signal.

Surely this depends on how the vendor sets their prices? If you're going to buy something from a website to test a stolen credit card you don't just get to make up your own prices.

And I think you may be over-indexing on the US "prices don't include tax" thing. Elsewhere, round-number prices are extremely common.

In fact a lot of the rest of the stuff in the post seems like it wouldn't work very well either. (E.g. you're flagging anyone who has done a transaction in the last 90 days outside the range of hours at which they have 2+ transactions? Wouldn't that be like 50% of people?).

It's unclear to me whether this article is an attempt at breaking down complex expertise into over-simplified SQL queries, or whether it is all speculative and made up.

There is a conflict between "Six SQL patterns I use to catch transaction fraud" and "Nothing here comes from anything I’ve actually worked on or seen".

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nswango 2 hours ago | parent | next [-]

The "transaction outside usual hour range" seems pretty basic.

I don't usually buy gas, coffee or snacks at 2am. But on the very rare occasion that I do, I'm dealing with some kind of personal emergency and don't also want to have to call my bank.

I get that that's also a time opportunistic thieves, etc, might be operating. But the cost of false positives is also a thing.

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normie3000 5 hours ago | parent | prev | next [-]

Worse than that.

Coffee usually _is_ a round number in my experience, and I know of people who aim for round numbers when filling their car, and of fuel stations which require a pre-set value, often 10, 20, 50€ etc

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sheept 3 hours ago | parent | next [-]

Yes, as your parent comment points out, the article centers itself on US transactions, where listed prices seldom include tax and are frequently a cent below a round number. For example, the menu says a dish is $15.00 but the restaurant charges $18.83 after tax and tip. Globally, there's no doubt the US is the exception rather than the norm.

	▲	panflute an hour ago \| parent [-]
		That sounds reasonable for some states but 5 states have no sales tax and many states have exclusions to sales tax. Many of those are also likely to have rural areas where small businesses like to use even amounts.

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Niksko 4 hours ago | parent | prev [-]

All of that is easy to account for, all of the metadata you need is available. This also applies to the sibling comment about rounding up to charity at the grocery store, the data is all there, even if it's e.g. the fraud analyst at the bank or credit card company instead of the fraud analyst at the grocery store.

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normie3000 3 hours ago | parent [-]

I don't need to account for it - I'm just stating that this doesn't match my experience:

> Real cardholders almost never buy something for exactly $1.00. Coffee is $4.73, gas is $52.81. The roundness is the signal.

	▲	nkrisc 2 hours ago \| parent [-]
		The article is about the US and your example uses Euros, so I don’t think your experience applies here.

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mike_hock 2 hours ago | parent | prev | next [-]

This is also

a) trivial to bypass by adding dither to the test transactions and

b) trivial to improve upon with proper statistical analysis and

c) shouldn't this kind of heuristic pattern recognition with no expectation of near-100% accuracy be what AI is good at?

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themafia 5 hours ago | parent | prev [-]

I'm seeing a few stores here and there which have a "round up to donate" option. I guess I'm a bit of a sucker and I always use that option. My groceries are always a round number as a result.

	▲	time4tea 2 hours ago \| parent [-]
		Ive always suspected that this is all of a tax dodge, a money spinner, and a pr exercise "we gave xxx to charity" - no, your customers did. Just set up a direct debit to your favourite charity.