I'm not sure how real estate law works in Poland now. I only have an experience with a studio apartment which was empty before even before viewing.
When I was buying a house in Canada my agent told me that the basic principle (give or take) is that if something is attached to the walls, floors or ceilings, and if it cannot be removed without tools such as a screwdriver, then it is a part of the house and stays put. Exceptions have to be clearly described in the contract. In my case, the previous owners had a TV set attached to a wall. I had to agree for them to take it with them.
The agent told me a story of a fella who sold a house with a rec room in the basement of the house. After the sale agreement has been signed, the seller removed interior walls, ceiling and floor coverings and turned the basement pretty much into bare concrete walls and floors.