in the words of the BFG (no longer posts on here - unless different name)
CANVASS
CLEAN
CULL
simples !
have the odd customer I let go to 3 cleans because of their work e.g. submariner, engineer on a cargo vessel, guy who travels to india / china importing stuff .......... all work away but all want clean windows for when they get home plus i give properties once over and email em if owt amiss.
3 years in and round settled and sorted and only odd customer last year binned for non payment or too slow payment