Just like San Francisco and Anaheim have tried to do in the USA, Barcelona is trying to make Airbnb responsible for the advertisements of its users, and is trying to fine Airbnb heavily for illegal ads on its site:
Barcelona’s town hall stated on Wednesday it would fine both Airbnb and fellow online rental firm, Homeaway, 60,000 euros ($66,918) each. If the companies continue to refuse to regulate their own users, the fine would jump to 600,000 euros each, a source from the town hall said.
It'll be interesting to see what happens with this -- in the USA there are laws which exempt online corporations for material posted by others on their site. Not clear how this applies or if it applies in Barcelona...but Airbnb is not a Spanish company, it's an American company.
Why not just fine Airbnb $1,000,000 per day and be done with it? I mean if you can pull fines out of a hat, why not aim high?