Sorry for the English post, my German is not good.
This is the dealer in which I bought the car 6 years ago and drove 120,000km (from 100kkm to 220kkm). I saw the car on the pictures, the price was negotiated, and then the car was reserved for me, for 1 day. They also shown as (after the deal) where the KFZ-Zulassungstelle is.
I never had any problems with the car. The only problem was with the test drive, as it was not possible (only around the dealer shop was possible). I hope they still sell good used cars.