Whats more interesting is the history of problems with other window cleaners messing them about, going missing then reappearing etc .
I always ask about the customers previous window cleaner because it gives you a bit of an insight into what the customer may be like.
IF they say "oh he just stopped coming" I think "He dumped her - I wonder why?"
Mind you thats not always the customers fault. I have picked up some lovely customers who have been dumped by other window cleaners for no good reason that I can see.
You used to get a lot of newbies who tried it for a while but found it hard work and packed in. Even so they could tell the customers. I do wonder sometimes.