“Thank you” seems to be similarly versatile in London. You can’t go 30 minutes without hearing it. Once when I was in a bookshop and approached the counter with a couple books to buy, the shopkeeper opened with “thank you”. To this day I don’t understand what that was about.
Part of the transaction is the performance of a service role - they’re thanking you for allowing them to help you. But also it might be a habit if they’re used to serving a queue of customers (“Thank you for waiting”) or just a polite verbal cue that the transaction has started or again the habit of saying thank you on being passed something hand to hand (often shortened to “ta”).
Thank you for buying their books
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