I have been caught out a couple of times with people asking me to do their windows, and after extra first time washes I do the second wash, only to find, when I collect, that they have gone. It's not always obvious that they have gone, because some lets are part-furnished. For this reason I have introduced a new policy for rented premises (as long as I know they are rented!). When asked to do their windows, if I'm not sure, I ask if they are renting, and secondly, I say that I am happy to do them, but there is a condition, which is that they pay for one extra clean, which I will hold, until such times as they leave or do not require my services. This I have done three times so far, and people seem OK with it. I give them a receipt in the form of an invoice, name address phone number etc, and write; "Received the sum of £xxx for payment in lieu of your windows being cleaned if you have left your rented accommodation owing me payment. This, of course, will be returned at any time at your request should you no longer require my services, and/or owe me money. Assuring you of a regular and reliable service at all times." I thought I'd pass this on as a recommendation to everyone.