Quoting: hello
The question is - do the stores in Polanda know in which store you bought the item?
with the returned goods you need to present a purchase document from the seller (an invoice, a receipt, a bill - in Polish "faktura", "rachunek" or "paragon"), and it's basically the only prove requiered to confirm the purchase.
Quoting: hello
In Poland - you can buy one item in one store and return it in another I think :).
Try it and find out, but if you get arrested for deceit, don't come here blaming me :)
you'd be doing it on your own risk and responsability (I'm getting americanized too much - writing disclaimers on obvious things)