I don't know the life lesson in peddling low quality products for astronomical prices where the only party really gaining any significant profit or gain is neither the buyer nor the end seller.
I'd rather my kid mow yards, shovel snow, or deliver papers if they want to learn about work ethic and making money.
Most of the items I've seen sold door to door by kids in my neighborhood are food related or magazines. I sold Tom Watt crap for boy scouts back in the day but they dont do that anymore. (thank God)
My kids, 7, and 9, help the neighbors with their yards, mow, and shovel snow because they like to help out the community. They usually get paid in chocolate chip cookies or home made pretzels from said neighbors (and are fine with it). Sometimes my kids will get a few extra bucks in their allowances also for seeing something that needs to be done and doing it on their own.