First I did not state that the sulfur in the water in Iceland was the problem, look at your inbox again. I clearly told you that the plumber SUGGESTED that it could be the sulfur in the Icelandic water that tourists are unfamiliar with and that I have heard this from others. Second, yes, on your account I had a certified plumber coming in on a Sunday and make a thorough inspection of the apartment after you left. That involves quite some cost as I am sure that you realize as you state you know a lot about buildings. The plumber found nothing wrong and made the possible assumption above. Third, I had my daughter Julia come in immediately after your late reply following your complaint and I told you I was very worried about the situation. It is my home and broken sewer is very serious. You approved her coming and check on the situation and she could not even find a hint of bad smell from sewers or anything else.
Fourth, I also talked to my neighbors in all the other apartments in the building and nobody has noticed anything at all. Obviously we all have the same sewer. Fifth. No guest before you or after has made this accusation.
Sixth, I have only 5* reviews and a super host status and I would not offer my guests or my family a broken sewer or bad smell.
Finally I feel that I did everything in my power to respond and react to you and your complaint but I find your claim for a refund faulty and your review inappropriate.