Sounds to me as though you need richer clients.

You've been doing this for 10 years, so I hate to offer advice since you're clearly more of an expert at this than I. But...

I would advertise on Craigslist.org under Services. It's free. You'll be getting the more progressive and savvy clients on Craigslist. I also would interview THEM and ask them what their history is with cleaning people. Be picky -- don't be too quick to accept a new client if they have never used a cleaning service before. Ask them how long they used their former cleaning services, and why they are looking for a new service now. Rather than take the first reasonable one that you interview, hold off until you have 3-5 potential clients, and take the client who has had the most longevity with their former service, and who seems wealthy enough not to be affected by things like seasonal factors.