Stayed a week at Alexandros' place and we truly loved it. Alexandros picked us up from the ferry and before dropping us off at his apartment, took us for a ride around the port of Serifos, pointing out where to find good grocery stores, restaurants and bars, etc.
Communication during our stay was quick and easy, and Alexandros always went out of his way to be helpful.
The apartment itself was clean and well-stocked with pretty much everything you need and more, had AC and an amazing view over the bay. In terms of location it's been great too. There's a couple nice beaches right within walking-distance, and also the port with its restaurants and stores is just 10 mins walking.
Highly recommend staying at Alexandros' place! No doubt we'd stay here again if we were to come back.