The kind of situation I'd expect to see more often in real life is that NPS scores are inflated for fun luxury goods, because they naturally inspire more enthusiasm, and deflated for essentials, because very few people are even capable of getting excited about socks.
Mostly I was meaning to hint at, where I've seen things like NPS go off the rails is when people assume they measure what the marketing pitch says they measure. The reality is invariably more subtle.
Recommendations are also skewed by the needs and interests of the pool of friends a customer has. I'd recommend (and brag about) a good computer keyboard or monitor to almost anybody I know, because 90% of my acquaintances spend a lot of time in front of a computer; I can make an educated guess about the small minorities who might be interested in a certain restaurant (location-constrained) or a board game or a bootleg CD; but I don't think I could "promote" to anybody things like old roleplaying games (I'm the most eager collector I know) or a graphic tablet (the handful interested people I know already have a good one).
And what about the buying potential of one's friends? Consider plants: students could help sell their student friends something inexpensive that fits in a small vase in a small dorm room, farmers could help sell other farmers enormous amounts of product.
Also the "Why did you give that rating" follow up question can help spot whether a significant number of people interpret the question differently. I've seen surveys for financial institutions where a lot of people write "I love my bank but I don't feel comfortable recommending financial products to people" which is another example of an individual's score not accurately representing their experience as a customer.
The kind of situation I'd expect to see more often in real life is that NPS scores are inflated for fun luxury goods, because they naturally inspire more enthusiasm, and deflated for essentials, because very few people are even capable of getting excited about socks.
Mostly I was meaning to hint at, where I've seen things like NPS go off the rails is when people assume they measure what the marketing pitch says they measure. The reality is invariably more subtle.