Even if you are present in an apartment yourself, it is still too risky to allow a complete stranger to sleep in the room next to you. How much verification can be done by you or airbnb? The Norwegian shooter had no criminal history that could have been caught by any verification. So how can you be comfortable with allowing a stranger into your home with no verification done at all from your side?
I think there should be a service which will allow you to rent the room only to your friends or to friends of friends but no further than that. This friend list can be from facebook, linkedin or Google+. This will reduce the chances of getting a rental but give peace of mind that you are not letting some hardened criminal into your home.