Hi DC
I know you addressed your question to SMP, but I'll throw my tuppence in (for what it's worth)
I identified an area for Paul and asked him to canvas every house, excluding those with treacherous overhangs and any other obstacles. He then blitzes the area and signs up as many people as possible.
Initially I was concerned that he'd go in at silly prices, but far from it. Most of the work he picks up is at a better rate than I would charge if I had done the canvassing. Occasionally I think he's slightly underpriced, but overall he more than makes up for it with the other houses.
When they've done canvassing, they hand you a list of all the people who've signed up, phone numbers and any notes (access, payment method etc).
I normally ring round all the customers to introduce myself (or get the missus to do it) and after that, you just go and clean the windows as normal.
Anyone who drops out in the first 2 months, Paul will replace for you. Or, if you think he's grossly mispriced you can ask him to canvas a replacement (but as I say this has only happened once in all my dealings with him)
As for speed, I needed to build up slowly, so Paul did the work for me piecemeal, now I've found a business partner with a bit of money to his name, I'm getting a lot more done in a shorter time frame. So it really does depend how fast you want to grow the business.
The only area that Doorknockers lose points, is Paul seems to take an eternity answering emails, so it's best to pester him on his mobile or with texts --- hope this all helps