The website that gave me the inspiration for my trip from Narvik to Singapore is Seat61. It recommended Real Russia as a good agency to use to book your tickets on Russian trains including the train from Moscow to Beijing. I could have had the tickets delivered to my hotel, but I decided to visit the office since it was only a few metro stops from my hotel.
The building. I used Google Map's Streetview to scout it out. There is a small blue building across the road which helped narrow it down which building it was.
Daughter and mother who are the local representatives. The mother did not speak English, but they were both very friendly and helpful. It was quite warm and they gave me a drink of water.
If you speak Russian, you can use the Russian web site to book your ticket and it will be less expensive. However, if you need to get a visa for Russia, it helps to get some documentation of your trip organized so that you can prove to the Visa people that your proposed trip is organized. Bookings for Russian trains open 45 days in advance.
Real Russia's service was fine and the tickets worked.