I've also knocked on the wrong door too, and have also done this deliberately on occasions when running early.
Householder answers the door and tells me that I've come to the wrong house, Mrs Smith lives next door.
Naturally I'm apologetic but add that if they ever need their carpets or upholstery cleaning, I would love to give them a quotation. I leave them a card and they know that they do not have to go far for a reference or to see the quality of my work. At a guess, I would think about a 50% conversion rate
The JAGUAR MX-2 ETM @ crossamericancorp.com