Bingo. And assuming somebody did actually have a really amazing and effective marketing strategy, they would be heavily disincentivized from sharing it. By its nature, marketing is about outcompeting other companies for attention and sales, so the less competition, the better.

So just based on bayesian probabilities, if you are reading marketing advice from somebody, it probably is bad (or wont apply to you). If you are reading a story about an effective marketing strategy somebody used in the past, it probably doesn't work as well anymore.

As you state, this doesn't take anything away from the entertainment value of the story, but it is just entertainment and marketing, not advice.