I'm throwing a vicious circle into the balance.

Unfriendly and absent customers produce unfriendly and uninterested cashiers, unfriendly cashiers produce unfriendly customers. The chain of evil can be broken by being consistently friendly, attentive and interested in the well-being of others. One takes up short genuine eye contact to the cashier and the bystanders, appreciates briefly the human being. One appreciates the thousands of times everything goes smoothly and does not exaggerate it when it is not so.

In public space, we are all equally good and bad role models, aren't we?

I don't say that specifically to you. But it strikes me that such stimulus reaction chains are actually quite simple to solve if one behaves surprisingly differently.

For me, this example was also a good reminder to stick to my own advice when shopping the next time :-)