I always charge min 3 times monthly charge on all my first time cleans ( domestic ). ie monthly clean £12.00 first clean £36.00.
By charging this way I dont care if they only want a one off clean or regular cleans, I have found most domestic customers are very willing to pay more for the first time clean.
I have found this way of pricing work to be a very good for my business.
I usually charge 50% more. It takes me more than 50% longer usually so I do lose out a little bit on the first cleans. I don't mind that if I feel that thgere is a regular job there. If someone comes out and says that they only want a one off, I charge double.