unhappy faces
...how about "serious"? It would help change the picture (and the mood) a little bit, and would be closer to the truth.
miserable assistants
...how about "serious" again? I am sure if you smiled at them, they would smile back, especially if you shop there often.
assistants in Kefirek
I know there might lots of shops with that name all over PL, but do you by any chance mean the Kefirek in Ełk? If so, I know the ladies, have often enjoyed friendly over-the-counter banter with them, and do not find them lacking in the courtesy department. Admittedly, they are not all smiles all of the time. But hey, we Polish peeps just ain't built that way!
:-D
Polish 'friends' who are only friends when they need something
no different from "friends" of any nationality... as opposed to real friends...
This just to show you that the things you dislike about Poland don't really exist :-)
BTW, Warsaw seems a beautiful city to me now after 5 years spent in London.