I don't think it is good advice. Maybe sales skills are useful, but the thing is, there are zillions of things one could learn before starting a business that could be useful (like getting a degree, saving enough money, ...). It is just one more thing that delays you actually doing what you want, and that is bad. Why not just learn on the job (starting a business)?

However, if you absolutely think you have to put yourself through that ordeal of selling crap door-to-door, perhaps collecting money for charities would be a better choice than selling products of questionable quality.