Every time I read some technical description about why this isn't happening, the technical description seems convincing.
However...
A friend tested the theory a few years ago. He doesn't own a swimming pool, doesn't want to, and has never expressed any desire to. He put his and his wife's phone on the table and said to the wife (loudly), "Why don't we look into pool fencing?". She agreed with him. Shortly after, on both of their phones, on a particular social network, they were inundated with ads for....pool fencing.
However...
A friend tested the theory a few years ago. He doesn't own a swimming pool, doesn't want to, and has never expressed any desire to. He put his and his wife's phone on the table and said to the wife (loudly), "Why don't we look into pool fencing?". She agreed with him. Shortly after, on both of their phones, on a particular social network, they were inundated with ads for....pool fencing.