@Alexander
I would hazard a guess that he does not own the apartments he is letting, and the landlord found out, it very popular in Poland to do this as I found out to my cost. Do you honestly think he was letting the property when a sale was imminent, so much so that the new owner had the keys while you were still there it would have been quite simple to request the new owner to wait until you had departed, before they took procession of the apartment?
I would write a review similar to the post you wrote and put a stop to this scoundrel's activities.
Additionally I would request a full refund under those circumstances, which believe me as a Host is a hard thing to write.
Regards
Cormac
The Explorer's Club Krakow III