i had 1 last time around, they were having a ridge tile replaced on the roof ( just the 1 ridge tile )
well it turned out the guy brought a "caravan cleaning brush " and connected it to the hosepipe and did his own windows ( with tap water of 470 TDS :

:

:

)
anyways, i arrive today and knock on the door to open the side gate
" oh great your here, our windows are really bad, they then explain that after the tile was replaced, the hbby decided to do them with this new caravan brush on a pole "
i expalin i use pure water blah blah blah and then explain it'll take a few cleans to get them as good as they were before
so i turn down the flow really low, quickly brush over them and leave then with water marks still on, its a big house and by the time i get it down the front is dry, it looks slightly better but not much, i explain again that it will take a while to bring back up to standard and chuckle to myself as they write a cheque

that'll teach them

, sorry to the folks who will cry " unporfessional of you " but hey, it made me laugh a great deal
