That’s pretty ingenious to call people dumb. This is psychology and these tricks work on you even if you trivially understand that 3.99 is not feasibly cheaper than 4.00 — your brain simply processes information non-stop in the background and you are affected by this. Hell, there was even a study that people who claim they don’t fall for these kind of marketings tricks are more susceptible to fall for this, so, take what you want from it.

Also, even knowingly false propaganda has an effect on you.