Have only been going 5 years but in this time I have learn't to work that I will turn-over 10% of my round in new customers, drops, drop-deads, movers etc...this also includes those who want a winter break...
I say yes but will treat them as a new customer with a new price and will need to charge them extra for the additional time the clean takes if I am able to fit them in as I am now full.
But as some of the old-sweats have said ...there are more people wanting a window cleaner than there are shiners...
This question of what to do when approached really depends on how your round is and what you want from it....
Customers are like cow's....milk them...wait then milk them again and repeat..when the cow stops producing either take it home as a pet or cull it.
Cheers and Happy Christmas
Dave.