Isn’t it way easier and way more damaging to just take a photo of him? Receipts aren’t even associated by name unless you’re picking up food.

True; a more realistic scenario would have to include "covert surveillance" (where you don't want to let him know you're watching), and even there I'm not sure much could be gleaned about any individual. In theory you could use that to build up a picture of someone's habits, in practice other techniques are better. Though... you could use that to spy on the store, actually. If you're a tax auditor making sure they aren't underreporting their sales, that could be useful.

But yeah, any idea I come up with to exploit that is always a bit of a stretch.