During 7 days in the apartment, 4 full days we couldn't use the terrace and living room (commons areas). She put another “guest” in that part and a chain on the doors (I have photo). Host didn't say anything to us even though she saw us in the evening, until I asked her in the morning why can we used it because we rent her apartment because of the terrace. Her response was rude and insulting. Didn’t even try to find a solution or tell honestly what's going on, just said if you don't like it you can leave. Her answer was that the flight for that “guest” was canceled (for 6 days, who would believe that?!), and of course, later we found out that she didn’t tell the truth and that there was no canceled flight.
If someone is wondering why we didn't get out after this - she ruined 2-3 days of our holiday, and didn't want to spend the rest of the vacation dealing with her, searching for another apartment, writing to air bnb…
The location of the apartment is good and it has all the amenities someone needs.