Let them go because they put off a few cleanings?
You won't ever make it far doing that. Having customers cancel is part of the business.
My questions are..... do you go in person to give bids? If not, this is probably YOUR fault. Going in person helps a lot.
Do you have a sheet that sets the rules for them? If you go in person you can give it to them at the time of the bid or if you don't go in person you can mail it to them the day they sign up for service so it gets to them HOPEFULLY BEFORE you get there to clean. Or, at the very least give it to them when they open the door for you when you get there to clean. If you don't have a rules sheet, this problem is YOUR fault.
If you go on a bid do you give them a sheet with the prices on it or do you say it verbally and expect them to remember what you say?
If you go to bid do you give them different prices for weekly/bi-weekly/4-weeks? If they sign up on your website do they get different prices for weekly/bi-weekly/4-weeks? Or ever how you do it.... do they get the different prices? If not, it is your fault. And make sure that in your set of rules they know that if they choose weekly and they go over 1 week their prices goes up to the bi-weekly price. If they choose bi-weekly and they go over then their price goes up to the 4-week price. If they choose 4-weeks and they go over then their price goes to the first time in price. If you don't already give them different prices this problem is YOUR fault.
Now with that said.... you must be human about it. Some people are going to go over a few days here and there and sometimes a person will need to be switched from week to week. But the time you enforce this rule is when you have someone that continually wants to go over.
See, you want them to do exactly as you want them to do but as a business owner you can't expect that to happen without rules. People think they can just get some customers, clean their house and it will be smooth sailing.... it don't work that way.
Once you get to be an experienced cleaner, you will see that the ones that say you do good work and appreciate you are the biggest PITA's you will have. When you are a solo operator you need to find the people who are at work when you clean and you never see them. Those are the customers that make you have a great day.