[icebraining]

So what? Are you giving thanks because you want a service worker to validate you, or because you are grateful to the other person?

Neither, if I give thanks it's to improve the other person's day. Giving thanks just because I'm grateful, regardless if the other person will appreciate or be annoyed, is just being selfish - making myself feel more virtuous without actually improving anyone's life.

I interact with many store clerks more than once

Ah, yes, I also have a friendly relationship with a couple of people, like the corner store owner, and I thank them habitually. I was speaking about people I only interact with once or rarely.