I'm surprised that a newbie hasn't come up with the idea of offering 3 monthly cleans for the same or lower prices and just leaflet everywhere in their vacinity to start and fill a round.
How well do you trust your customers now some of them are worrying about job cuts with more doom & gloom to hit the news making customers twitchy.
now theres an idea 
I would say that the majority of my domestics would love it if I only came round every 3 months. As long as they have a window cleaner that comes round when the windows are dirty, they would be happy.
Now if someone sets himselfe up on a cleaning by appointment business he could make a killing.
Dial a clean would go down really well with most people. No good for us though.