Is there one person working at each flat at a time? How does it work, do you phone up and book, same as an independent?
I've not used a parlor and don't really like the idea.
It's very simple, either select who you want to see from the rota and make a booking. You will then be directed to a flat where the WG is based.
Alternatively, call and ask who is available at the walk-in location. If you want to punt with any of the WG's at that location either make a booking to ensure you can see who you want, or turn and take your pick from whoever is available when you turn up. They only offer a walk-in service at one location.
