That very much depends on where they're situated Vin, if it's in the middle of an estate surrounded by other cleans you could be making a rod for your own back, these neighbours will no doubt talk, quite possibly have a neighbourhood WhatsApp group, and if you let one dictate when you should clean, others may feel they can do the same. I would have a conversation with them, explain you can miss it this time but in future if your to keep them on the books it has to be every time,, "I never start a job in the rain but can't be accountable for what happens afterwards, weather forecasts unreliable etc etc. I remember making a similar mistake in my early days, there was a huddle of people talking and one came over and said can you do mine every other time, to which I reluctantly said yes, she went back to the huddle and with that 3 others neighbours requested the same, it wiped off £500 from my turnover because I was growing the round and eager to please. Its not easy when your growing your business but you'll see the benefit in the long run, your way or no way.
Edit.. I've had a few not today's and I've let it ride because of the present climate but if someone where to use the weather as an excuse, particularly the weather after I've been then they're definitely not the sort of customer I want. It's a ridiculous excuse, if it rained whilst you were doing it then you can see where they're coming from but we're in the UK, it WILL rain on their windows after you've been sometime, guartenteed.
I see this regularly on here about customers having chats about their window cleaner and ganging up on them. I can say with 100% honesty that the subject of window cleaners never, not once, came up in any of the thousands of conversations I had before starting out in the business. Not once*.
Maybe everyone else's customers have nothing else to talk about but it does seem odd.
Vin
* [edit] I think I may have asked a neighbour once after we'd moved who they used.
Whilst i agree that we as window cleaners are by and large quite an insignificant part of peoples lives, i am conscious that like a lot on here , i don't advertise anywhere, not even on my van, all my new work for donkeys years has come from recommendations which means there is a network of sorts, this person knows that one etc which is an obvious by product of recommendations, so if you have exceptions to rules, you really have to be prepared to offer that to everyone if asked, and i really don't want to. Iv'e got a formula that works for me and its much easier if i stick to it. Then again i'm a sole trader and intend to stay that way, i imagine if you employ, then there's a a different mindset, and you have to be more active in looking for more work with more overheads.