I don't think sales, in general / in principle, has to be immoral. There's shades and details etc. We can argue value to business vs value to consumer, but in general sales, there's nuances. But we are not talking general sales here - we are talking door to door salespeople specifically.
The article focuses on the sales person and for reasons of focus or otherwise, ignores the heard of elephants in the room - what happens to the buyers afterwards.
Vast majority of door to door sales is predicated on anything from severe informational asymmetry to outright fraud. It has to be - there's a REASON why they're paid so much per sold account. It's hard work and it's swimming against the tide. From experience, they are trained and incentivized to find a weakness, with ferocious persistence and evolving methodologies, and will thus statistically exploit those with weakness. They pray on the very best of human emotions and instincts - unwillingness to be rude, eagerness to be friendly, to relate. They build and exploit implicit trust. Their product is by definition not good value - if unconvinced, imagine same product but for the price minus the salesperson commission. As I mention in more detail in parallel thread [1], nothing about average door to door salesperson is real - they're not your buddy, they will not hold your hand through the process, they will not be there to help you or answer your calls if/when things don't work out. As primary outcome of their endevour, they collectively reduce our trust in each other and faith in humanity.
(And like anything else in the wide and exciting world of MLM-likes, there's layers. Not only do the salespeople target the elderly/vulnerable, The door to door salespeople themselves are targeted to be recruited from specifically vulnerable or impressionable, and overall success rate of the profession is lousy. Very few doctors or engineers become door to door salespersons - a struggling minimum-wage worker or a new immigrant are the typical pools; I was the Venn diagram of both. I don't expect your friend to relate the true nature of their job to you, or likely even to themselves. But see if you can talk to their average buyer and get their thoughts).
Want more? Tune in the next episode of the grouchy cranky old man, where I rip into real estate agents :=>
1: https://news.ycombinator.com/item?id=33718726