Been silently sitting reading this thread with great interest.
I too am soon investing in a gutter vac and have been considering how to market it.
To the residential market, apart from your window customers, door knocking has to be the way. I think that a 5% success rate at knocking (5 in a 100) would be achievable, at an average price of £50 per house.
For those who have actually used this on a house, what is the time spent including set up and down to complete a clean?