I've seen some pretty crazy stuff myself. They have access to more than we think and use it.
I rented a jackhammer at Home Depot once. No joke, I then started seeing Google ads on all the sites I visited about tool rentals. WTF? Now guess in this case it's Google buying info from the credit card company, or perhaps the store itself? But it's no coincidence that I rent a tool and start seeing ads about rentals not long after. Kinda creepy. I have seen similar situations like this before where a IRL action triggers certain ads.
While this technological world has it's positives, one negative of it is we do not have any privacy. I guess it's not bad if you have nothing to hide. All our moves are tracked through money transactions, web transactions etc...
One reason I run my own email server though, at least I have full control over who reads them. Well, sorta, if I send it to an untrusted server then I guess I don't have control from that point.