Tosh, I started w/c part time when I was selling health insurance (self employed) and selling office printer laser cartridges (self employed).
In 2000 I decided I would have to do one job as I felt I was fiddling about with all three. My Health Insurer (WPA) gave me an ultimatum - shape up or ship out -I shipped out. I lost a huge laser printer supplies contract (on price) to a Police force and handed over my few remaining customers to a friend in the business. I would never go self employed sales again.
I have done double glazing sales in the past too!
My experience of self employed sales is that you get the managers who cream off the "best leads" plus one or two "driven" high flyers and then the rest of the guys faff around in mediocre land because they're fairly bright, think the grass is greener or haven't got a good paying job because of lack of formal higher education/redundancy.
If you want motivation decide you are going to have a day a week like Roy Harding - to do that you need the qualities of a sales person - drive, the ability to handle rejection and focus.
If you're going to sell then sell your wfp services to top end customers and reap the rewards!