Worth a read, particularly the part about loyalty cards.
I saw the future of advertising, and damn is it scary
https://www.androidcentral.com/i-saw-future-advertising-and-damn-it-scary
QuoteWhen I stuffed the band into my NFC shielded wallet, the UHF reader picked up the tag with no problem
I refuse to carry loyalty cards. If there's a really good deal, I will enter my account by giving my phone number, but usually I just pay extra or, in the case of my grocery store, refuse to shop at the one in town that only gives special pricing if you have a card.
The other grocery store in town tried it, and the feedback was vicious and immediate - people said "That's the reason we come here in the first place" and they had to back down. Which shows one thing - if people cared about privacy enough to walk out the door without purchasing, this practice would end.
It's shocking how little it costs to buy someone's "loyalty"