Based on TripAdvisor reviews, I booked a one-way trip (Fira -> Oia's Amoudi Bay) for a party of 6 with Captain Stathis on the Anemos over email, for a 20 EU deposit paid via PayPal (total price quoted as 120 EU for up to 10 passengers). Captain Stathis responded promptly to questions, and suggested stopping for a swim in the hot springs or a secluded bay along the way (no sand beaches available en-route).
I checked in the night before the trip via email. The morning of, his wife Annie sent a very polite and apologetic email telling me that Stathis had called from the port with news that it was too windy to safely make the passage, and that he'd meet us at Fira docks to help with alternative plans and refund the 20 EU deposit. Captain Stathis found us as we disembarked the tender from our cruise ship. The water was incredibly choppy, and the ride over in the large tender had been rough. He advised against taking a water route on the Anemos, saw us to the funicular (also advising against the donkeys), suggesting a taxi or bus from the top, and refunded my deposit in cash. It was clear that Captain Stathis knew the local waters. He showed integrity by canceling a lucrative appointment with some strangers coming off of a cruise ship, rather than having my family risk an unpleasant experience -- and expense -- on a vacation that we'd all been looking forward to.