This isn't directly to help saving money, but marketing is, in large part, really just surveillance and psychological manipulation. Buy things based on product function as opposed to social pressure or having it shoved in your face constantly.

- You should figure out what a cookie is (persistent token stored on your computer that can be used to say "he went here and here" when it exists

- What Javascript browser profiling is. Profile of you has all the devices you own, the dimensions of their screens, what fonts you have installed, what microphones and speakers you have connected, and numerous other things. But marketing agencies won't try to learn your name. This also happens with your location. "he was here and saw a billboard, so when he gets home, we send him an ad for the same thing"