Im with Ian - window washers.
I work in light rain/drizzle to stay on time. I turn up on time no longer than a week late.
If the customer doesn't want the windows being cleaned for whatever reason thats their choice (but if it happens regularly then i drop them)
As im always around regardless of the weather they cannot say im not regular or reliable since they always see me.
If they are not in then the windows get done lights rain or blazing sun - it just gets done AS AGREED at the time of quotation.
Im i know im gonna be late (over a week) for whatever reason then i will call them to let them know as i have promised at the time of quotation.
If im going on holiday - then i normally say my van is in the garage or something like it (people dont like you taking holidays! you get more sympathy if the van is in the garage

)