you are slap bang in the middle of the country i would do as you said leaflet, canvass, 30 mile radious gona be lots of houses!,
always be carefull when buying work, window cleaners will only sell what they dont want anymore, ie , access customers,underpriced ,area cant be expanded anymore,which is ok if you are starting out,just dont expect anything amazing unless u are paying top dollor,also be carefull only buy it if you can trust the guy, dont forget if he cleaned mrs blogs cony roof for free every other time, if you dont do it she wont be happy.
i once bought a round one of the customers had her frames,pvc and doors properly cleaned (this was when i was trad) for £1 more

it was every other month she wanted this,after once or twice i nicely explained that what she was having was very under priced and i dont know how the old windy could absorb spending an xtra 30 mins work for £1 guess what ..........she canceld
