First of all. before you discuss price, always ask how often they want their windows done. Make out that is a fabulous option that you and you alone offer, no other window cleaner is this flexible. By telling you a frequency they more or less agree to having their windows done.
I don't put any extra on because my prices are high anyway but the flexibility wins you customers and gets you referrals. I must have got 20 referrals last year just based on flexibility. Lots of old ladies want their windows done but cant afford every month. A customer is still a customer.
With George it really doesn't make any difference what the frequency is you just print a worksheet and who ever is due is on the list.