I was going at first to agree with you based on my experience with Berlin: when the ads there give a particular date in which the apartment will be shown, those interested have to fill a form right after seeing it. So in this situation there's no incentive for the owner to check the e-mails.

However, that doesn't explain why both the Italian girl and Hanz from Munich got over a 90% answer rate - if they didn't check the e-mails, the response rate should have been lower.

So while I agree about that one flaw, I don't really think it affects the results that much.