In my years of using Airbnb worldwide, I never had to write a negative review -but felt I owed this one to my fellow globetrotters.
1) Failed pick-up: The host organized our pickup at the airport, but his driver never showed up - although our flight was on time.
2) Complicated checkin: I had to sign a contract.
3) Internet: I was given a wrong password (missing upper case).
4) Smoke in our balcony and apartment from the bakery downstairs: We had to leave the apartment with headaches after 3 nights there (originally booked 7 nights).
5) Money back: The host offered to pay us back the remaining 4 nights but wanted us to cancel the reservation first. After double checking with Airbnb, it turned out that the common practice required us not to cancel our reservation - but to change it - which we did. We got our money back.