I never fault anyone for not smiling, or for not making eye contact. Some folks are introverts and some folks had it pounded into them as children that they aren't allowed to make eye contact with adults, and when they became adults they never learned how. And then there are autism spectrum folks that simply can't make eye contact.
As long as they are friendly, and talk to me or respond when I talk to them, they get perfect marks from me. If they are rude, or sneer, or mutter unkind things under their breath, I take a different approach. If I know them from previous shops when they have been great and friendly, I ask their manager (AFTER I leave) if they are having a bad day, and put that they didn't talk much on the report. If I don't know them, or if they've been rude to me on previous shops it's pretty much no holds barred. I'll rake them over the coals.