There is no way to compare to what is normally expected from an airbnb host with Kwstas' kindness and availability. He constantly got out of his way to help us, would answer in the matter of minutes every time we'd have a question but would stay discrete enough so that you would still have your nice romantic vacation !
His house is as close to the sea as you can get and one can even have the priceless chance to get asleep with the delicate sound of the waves in one's ears. The small rocky beach at Seralia was perfect to go swimming in the morning, before getting breakfast on the terrace, or for a last bath before dinner (naturally, on the very same terrace).
There is no place on the island we'd rather have stayed than Kastro, in our opinion the nicest and most beautiful town on the island of Sifnos. Some people might prefer Apolonia or Artemona for amore lively atmosphere and a more central experience and a better connection with local transportation (and less steps maybe...) but for us nothing would replace the local atmosphere of Kastro.
It might be a better idea to never talk about it to anyone so as to keep this gem a secret, but it would not give justice to Kwstas' house and his niceness, a true example of the impressive Sifnian sense of hospitality !