Over the years I've had a couple of times when someone has either collected my money from the odd unsuspecting customer or turned up randomly and cleaned their windows, claiming that they've taken over from me. It's only ever been here and there as they didn't have a list of my customers, so it hasn't been a serious problem. Very irritating though at the time. Those that payed the wrong person reluctantly paid me as well as they realised they had been conned and it wasn't my fault. However, those who had their windows cleaned by the trickster didn't want me doing them again, so I lost out that month.