I'm always wondering whether the people that I stayed with when I used airbnb declared the rent I paid as additional income and paid the taxes. In Germany at least I guess they would have to get a tax number from the authorities and pay local and federal taxes. There is actually an article on taxes on airbnb (https://en.airbnb.com/help/article/481), but I guess most hosts conveniently forget that they have to pay taxes. Otherwise there would most likely be far less people offering rooms in their flats if they would have to handle all the red tape.

Many guesses, no numbers, unfortunately. I'd need some numbers to really make up my mind.