The 3 stars are the result of the 5 stars for location and the apartment, combined with 1 star for what we found out during the check in.
We had the main window open all the time because The lock was broken. Making things worse there was a scaffolding right in front of the balcony so everyone could have enter in the flat while we were out. Not very safe - especially during the days of a big festival like the Primavera Sound. Moreover the morning after we arrived, and for the following 2 mornings, we have been waking up by the banging of hammers from the apartment under renovation below ours.
One would expect at the very least a message before the arrival notifing these inconvenients.