It seems even if you have a small SEO company and offer work from your home, which can be referred to as 'Doorstep Selling', you may need the legal documentation of a 'Notice of Right to Cancel'.
Seems a little extreme, but I have it on good grounds.
What does this entail, well it means instead of offering your services and carrying out the work and then wishing to be paid; somewhere in the middle of all that you should have got your new client to sign a Notice of Right to Cancel. Otherwise you could be leaving yourself open to firstly, none payment and secondly legal action if your new client is so inclined.
It's not the end of the world though as a simple form like this could solve all your problems and allow you to sleep soundly at night.
If you're interested in the subject or just want to find out a little more, here's a site full to the brim with information on Doorstep Selling.