You knock for your money and a stranger answers the door
This is where you slip into super-salesman mode . . .
YOU Oh yeah, she'd mentioned she was moving out soon. She said she'd recommend us to you, and to just keep doing them. Did she not leave one of our cards (show one) like this in the kitchen?
HIM Don't know what you're on about, mate.
YOU There's obviously been a misunderstanding somewhere, she's probably forgotten to mention it to you amongst all the stuff she had to organise for the move. Oh well . . . How about we give you the first clean free? (cos it looked like you were getting bumped anyway!)
HIM Oh you are wunnerful - I'll tell all my friends, get you to do my work's windows and let you marry my sister that owns a pub! - or words to that effect!