"Little do they know" (I loved this phrase, so popular with writers of cheap mystery fiction) "that the transaction would have gone through, but they would think it had been cancelled. So they get you to do it again."
I know what you're thinking. I thought the same thing. When I recovered the power of speech, I repeated what I understood him to have said: the little screen can say "Transaction Cancelled" even when the transaction has gone through.
"Uh huh," he said cheerfully, "sometimes it will do that. Sometimes it will reverse automatically. This one might have just slipped through fine, but the [terminal] showed it's been cancelled."
I asked for his supervisor. This chap, who described himself as "a credit card specialist", told me that "with some merchants and some machines there are ways to do multiple transactions when you have only swiped the card once - duplicate transactions like this are common".
This was beginning to smell like a story worth more than $24.03, so I rang the people at the bank who deal with media inquiries. Disputing a credit card transaction is one thing, but the call-centre people seemed to regard what had happened as unremarkable and I reckoned it exposed a gaping hole in the bank's processes.
The chap in corporate communications couldn't have been more helpful. He got his best boffins on it and was back within hours saying I had made two separate transactions at 9.16am and 5.28pm.
"Pull the other one," I thought, though I said something more polite, suggesting the same transaction had gone through twice and the second was held up for a day in some electronic limbo. "Well," he replied, "they tell me there is no scenario that makes that possible."
This is the point at which your correspondent blushes and looks for a hole to hide in. I rang the store, whose accountant had spent some time tapping keys on his computer and produced two invoices, bearing the time stamps ... erm, 09.16 and 17.28.
Each was for $24.03 and each listed eight items. The two lists were entirely different and, thus prompted, I could remember each of the shopping baskets.
Apologies were made and $25 in cash restored to the greengrocer's till. Yet, as the blushing faded, I couldn't help saying "But ...". For in the process of investigating a merchant or bank error that turned out to be illusory, I had been given several extremely casual acknowledgements that what I suspected had happened to me was a "common" occurrence and that "sometimes" this double charging will reverse automatically. Meaning that sometimes it won't.
"I think the help desk operator might have overstated how frequently this happens," the comms man replied when I emailed about this.
He conceded if a reversal was not received by the cardholder's bank - a "very rare" occurrence - the original purchase could be debited from the cardholder's account.
"The merchant will not know this has happened [as they have a 'transaction cancelled' message] so they would start a new transaction with the cardholder."
To sum up: a problem that is somewhere between "very rare" and "common" means you can get charged twice for something you bought. Sometimes the system corrects it; sometimes it doesn't.
The moral, of course, is to inspect your card statement - more closely than I have been in the habit of doing. "Tap-and-go" cards are already almost old-hat now; the "digital wallet" in your smartphone is at hand.
That means more opportunities for error and malfunction - and not just in the operation of my memory.
