I have the same question.
I am from Serbia (close to Greece) and had an idea to buy apartment in Greece for renting only.
It seems so far airbnb renting was out of tax system totally, and now they want to change that:
(because I am a new user, I can't put a link in the post, but there is a news about that, this is the headline - Greece to tax short-term rentals via Airbnb with 15%-45%, and the platform with 5% per transaction , you can google it)
Any of the Greek host can say something more about this? Did you register your airbnb property somewhere, how much do you have to pay, and all that..