In my T&C's its a regular service, if that is what was requested at the time of quotation.
If they say not today, i give them one more chance in the year, if they say it again, then they are advise that at the time of quotation its was agreed it was a regular service and a price to that effect.
If they want a bespoke service then a new quotation is required.. Basically a first initial clean price always.
Of course customers are totally entitled to say when they want their windows clean, but im trying to run a business which is my livelihood.
I dont need the hassle of picky customers there are plenty out there that need a regular service, if they want a 'as and when' service they can pay me extra for it (compared to a regular service), or dont have me to do it.
With regards to customers saying i have 'X' amount of window cleaners in the last so many years/month, i tell them why that is.
1) They are probably not professional window cleaners and are just seasonal or benefit cheats etc.
2) They vastly under quoted at the time of quotation 'just' to get the business then realised this. (which is why you get so many saying ' my last WC charged me this price - yeah? then why you asking me for a quote - speaks to reason really)
3) Or the customer wasn't good at paying on time.
It really opens their eyes. Maybe they dont like me saying it, but i believe in being up front with people and hopefully people appreciate this from me.