I had the same experience. In fact, I tried to contact the who-is registered user first and when I had no luck, engaged Sedo. I spoke to them after I signed up (my mistake) and they basically told me the only way to contact them was the same way I had already tried. The only use of their service was the domain appraisal. After I finally did get in touch with the domain owner (myself I should add), their appraisal was the same as the amount the owner wanted… so that was at least reassuring.