What's an example of this? I'm generally confused by your claim, because I've used a whole lot of internet and literally never bought anything through an ad.
If you are desperate and someone is able to convince you that he can solve your problems for only 20-50$ no questions asked, next day in delivered to your home wouldn't you click if you had the money?
Do a Google search for X accident lawyer, where X is literally anything, and you'll see what I'm talking about.
The most expensive targeted ads prey on the desperate. Personal injury, bankruptcy, addiction, jail, death and next of kin, cancer, you name it. Think if the worst possible things that could happen to somebody. Those are the most lucrative ad keywords
As dumb as it sounds when put like this, it actually works. When you start looking for it, marketing that exploits body image insecurities is particularly common.