I have also heard discussions on the rise of the double thank-you in American English. For a long while, the acknowledgement response to a "thank you" was "you're welcome". But during the last century, it has become more common to respond to a "thank you" with a "thank you".

Usually, in a retail setting, this isn't exactly an even exchange. The business says to the customer "thank you [for your business]" and the customer says to the actual person wearing the employee mantle "thank you [for serving me]". One does not thank an ATM or vending machine, but it is appropriate to thank a human bank teller or retail clerk. We know that the employee has no personal reason to thank us for our business, and we also know that the cash we pay at the register is thanks enough for the corporate body. So we thank the person in front of us.

Implicit in all those little, minor thanks is the acknowledgement that the recipient has the capacity to appreciate gratitude, however minor it may be, and may not get it as often as it is deserved.

This is slightly related to the peer-to-peer double thank you. In that case, each party is thanking the other for their participation in a transaction that yields a mutual benefit. A talk-show host thanks an interviewee for filling airtime on the program, and the guest thanks the host for the use of their distribution platform, or perhaps for the opportunity to show off their temporary fame to their friends. A person selling his car thanks the buyer for trading up from used car to cash, and the buyer thanks the seller for trading up from cash to used car.

This has become so prevalent that saying "you're welcome" in response to a "thank you" now implies that the act was altruistic, which may make those averse to bragging slightly uncomfortable. That would result in a more deprecating acknowledgement, such as "it wasn't any trouble" or "no problem" or "I'm just happy to help".

It seems that the article is saying that in India, a "thank you" is more akin to "this concludes our business for today; please send me your invoice, so that I may settle our accounts". That does not translate to the typical American use of "thank you". It does also translate to that, sometimes, but those uses are marked by intonation and context.

> One does not thank an ATM...

Ever use an ATM with voice prompts? It's hard not to talk back to a machine that's talking to you.

It seems to me that the service-oriented "thank you" is more about expressing satisfaction than gratitude. It's a way of communicating that you have no complaints about the service without suggesting that there could have been anything to complain about. When a person doesn't say "thank you" it implies they were unhappy with the transaction and that they may be less likely to want to do business with you again.

> "That's what I understand if I see "Thanks" instead of "Many thanks!""

That probably says more about you, or the particular dialect of your region, than him. "Many thanks" is not the predominate phrase for expressing thanks anywhere in that I have been in the continental US.

"Thanks" is only passive aggressive when in a context that makes that clear. It is most often used sincerely. That word alone is never "the tell" for insincerity; something else about the situation is.

You see "Thanks" as passive-aggressive? To me it reads as a very straightforward statement that communicates a moderate level of real gratitude.