It can go both ways. When I was researching for the next car I was going to buy, I started getting a _ton_ of car advertisements; however, most of them were useless. What their simple algorithm failed to notice is that I was looking at a very specific class of cars, and I spent more than 1 hour on several manufacturers websites doing research and had mostly narrowed in on my choice. The proper move would be to see that and advertise different dealerships to me, but I only got ads for other cars that I already decided I _didn't_ want.

Also, I like to research, in general. Which means I can often come across and get deeply into some very odd subjects and it seems there are some odd correlations out there in society. For example, after doing a bunch of research on different world religions and their origin stories, I started getting ads for the Mormon church, and strangely, for all types of gambling websites, destinations and attractions. None of this advertising was of any use.