Just go to this kantor: conti.waw.pl/cennik.php
They are currently offering to sell euro at 4.155, which is the rate announced by the National bank of Poland today
nbp.pl
If you are buying several thousand euro, they will drop that to 4.150.
It is a win win situation for both of us.
The risk of being robbed or getting fake notes for the sake of getting 0.005 difference in the exchange rate simply isn't worth running. Even when buying ten thousand euro that's fifty zloty. If I had the choice between maybe getting fake notes and possibly getting robbed due to being in a known place with forty-one thousand zloty in cash in my pocket or paying 50zl, I'd pay the 50zl.