We had a wonderful trip to Oia, thanks to John and this beautiful cave apartment. Similar feedback to everyone else that there are lots of stairs, but if you're planning to stay in Oia, you should be expecting lots of stairs!
John was always very quick to respond and took us to and from the ferry port. The apartment was exactly as shown in the pictures, very clean and it has an amazing view from the patio! The patio is shared with the people next door, but we didn't have any issues sharing the space.
If you are traveling to Oia, we highly recommend you check out these restaurants: Roka (traditional Greek), Karma (traditional Greek), Pitogyro (gyros), Hungry Donkey (crepes)...and the sunsets are amazing, but to avoid the crowds, you should watch it from Amoudi Bay.