When I was in the Canary Islands a number of years ago I learned an expensive but valuable lesson about sales as I was convinced to pay far too much for a zoom lens for my then-brand-new camera. The lesson was: they are professionals, and I am a rank amateur. The same is true of sales generally. Which is why the whole Facebook-Cambridge Analytics debate is in reality nothing new, and is, in one way or another, very widespread, as this article shows. Sales is ultimately about psychology, making you feel a need you didn't know you had, and making you willing to pay something or (in the case of elections and referenda) do something. The only way to prevent is is to stay out of the store. Don't go into that expensive camera shop, block ads on ad-supported blogs, and for goodness sake, don't use software that tracks you using a network of ads and logins.