I have been done loads of times, people just move without paying.
Even when they have paid, some don't tell me they are moving.
Many is the time when a new face comes to the door with a puzzled look. I have to apologize and explain that the previous owners didn't tell me they were moving.
I once worked with an older guy, [not as w/c] He insisted that the money was paid up front.
The customer said, "I think you have a bad impression of me" Kenny the old guy said, "I'm sorry, but any impression I have of you, is the one you gave me ".
A classic and I never forgot it. Dai