I turn it back round on to my ex-customers. I have a few that stiffed me for payment a while ago. At least 3 of them have recently asked me if I could clean them again for them.
My answer is always the same: Yes I will, happily, when they have paid what they owe plus payment before clean.
Strangely, although all have promised to pay, they haven't yet got to the part where they have handed over their money, so, still no clean, still minging windows, and a still unpaid but grinning window cleaner!
John