Hi,
I like the site, it looks very good. I'd trim the portfolio though. I can't speak about the German language names, but some of the English are, err, mediocre, and for me dilute the quality of a professional looking site. I think it would look better with just your very best names, and maybe the others listed somewhere else.
I've only had a quick look, but couple of other things came to mind; Your "Domain Topics" menu would probably be better named "Categories", and I wonder if a 15% surcharge for an escrow service might be seen as a bit steep?
Welcome to np, good luck