Makes me laugh how people on here think they are businessmen from Dragons Den. You are supplying a non essential service to people - how you can possibly drive prices through the roof by adding percentages here and there for infrequent cleans is beyond me - a couple of pounds maybe. If you were providing an essential service such as boiler repair, burst pipes or whatever then yes because you are in control and the customer has no choice provided the market is not saturated with competition. But cleaning windows - get real!
I more or less agree with Dave here, it doesn't bother me to be honest whether I clean 4 weekly or 8 weekly, half the time I'm so busy I don't get around on time anyway (not with the residential cleans).
I'm earning good money at what I do, 8 weekly or 4 weekly doesn't make a lot of difference in the time it takes to clean a house, in fact I don't think it makes any difference at all.
It can depend a lot on the location of the house, on the side of a busy road, or surrounded by trees and hedges, exposed to lots of wind and so on.
On a ten pound house I might put it up two quid if I thought it justified it, and would certainly increase the price if they went to 12 weekly.
My price are by and large very good anyway, if I put a £35 house up to close to fifty quid a clean I am pretty sure of the reaction I would get!
Ian