All the apartments I went was in the center.
I tried to go to one in a suburb linked with the tube, but I couldn't find the place...
I don't remember a "Marina", but you know they could say another name. Furthermore it was a few years ago, so I even don't remember the name...
I always call them first to get the adress and I always speak in Russian never in English...Even if my Russian sucks, they could understand me and I could get the adress...
In some apartments they might agree to send a girl to your apartment, in some not. Last time I was there, however, they seem to prefer that you go to their place than sending someone over...