My contracts or service agreements have a 30 day cancellation in them. If they want out or I want out no problem. I don't do agreements to bind anyone to me or my business. You hear it all the time people say "well I don't want to bind or force someone to stay with me so I don't need an agreement or contract.
Again... that is not the reason. The reason for the agreement is so there is a clear understanding of what work is to be done and what is included. (Scope of work).
I also have an initial clean up fee. For instance if someone calls to have a quote and the property is a mess...then it is going to cost X then X per month for 12 months.
That way you don't clean up the place and then they cancel and your screwed. One more thing...when you bundle everything your in control and you would be surprised what you can sell when its all bundled into one monthly payment.