@Daniele331 the problem usually isn't so much the promotion of new listings (that is always going on).
The bigger problem that causes slower business for hosts is the number of listings in a city growing faster than the number of guests traveling to that city.
I don't know how many listings there were in your city last year, but currently there are over 20,000 Airbnb listings in Barcelona. That is a lot of rooms to fill, and there might not be enough new Airbnb travelers to go around.
In our city (San Francisco) like many cities, there has been an ongoing effort to regulate Airbnb listings. (This being Airbnb's home city.) Eventually, the city did manage to gain enough leverage, and it caused half the Airbnb listings to be eliminated. This, of course, was very bad for the hosts who lost the ability to host.
The silver lining is the remaining hosts have a much easier time filling their rooms.
If Barcelona is experiencing an explosion in Airbnb listings, but the number of guests who use Airbnb does not grow by the same amount, hosts will see lower business. It is the nature of competition.
And competition can be brutal.
If you have a lot of good reviews from happy guests, you have an advantage that new listings cannot match once their month of extra promotion is over. Keep your price competitive, offer something special, and keep being a great host. That is a sensible answer to competition.
But it will be very tough until the number of travelers grows to match the number of listings. (Or enough hosts remove their listings due to insufficient business.) Eventually a balance will be achieved, one way or another.