Just to be clear, the lady who called from the vendor’s store did NOT ask me for any card details at all. She just wanted confirmation that I was kambuckta Smith, and that I had in fact ordered a clothesline.
That was it.
Considering the possibility that a random dude ordered a clothesline from that vendor in the last few hours, you were probably OK in responding in the affirmative. 
Australia’s Clothesline Killer remains free and unidentified at this point.
Right, I’ll agree with you there. I don’t know if there’s any good solution because your logic also applies to this:
The vendor has no real way of knowing if the customer is who he says he is, and the customer has no real way of knowing if the vendor is who she says she is.
But if we don’t do anything, we all could lose a lot of money to scam artists. I think the customers are generally better protected because they can do a chargeback with their credit card company or report it as stolen. Vendors are pretty SOL, though. We have no protections at all.
I find the algorithms interesting and sometimes I can figure out what set them off.
Once I had my car repaired, my mechanic does the auto repairs at a local gas station. The bill was $393.00 and he sent me into the gas station convenience store to pay.
The clerk glanced at the bill and ran my card for $3.93. I pointed out the error ( I like my mechanic ) and he voided that charge and rang up $393.00 I did suggest that he leave it and just run the card again for $389.07 which caused the guy’s head to spin in confusion.
That got the card locked. Supposedly the red flag is the small charge followed by a large charge from the same vendor. Probably would’ve happened regardless of the exact amounts.
Then there was the time I booked a spot at yoga retreat hosted by a small company in Texas. Since I was living in NYC at the time, I can see how a $1500 charge for health and wellness services halfway across the country would raise a flag and I’m glad they checked, even if it was a pain in the ass at the time.
My favorite one has to be what happened right after I purchased my first Kindle. I was excited and wanted to load it up. So I opened my computer and started buying books. FYI, when you buy multiple Kindle titles you can’t add them to a shopping cart and buy them all at once. Each book is run as a separate transaction.
So I was buying books, then I started to get emails from AMEX about the transactions being denied. I called them. Apparently, if you make 12 transactions in less 2 minutes they consider that suspicious.