The Psychology Of Gullibility.
I couldn't resist a lecture with that title, now could I? It wasn't even the hoax I half expected it to be, but rather a discourse by Cornell's Head of Psychology, Thomas Gilovich on the causes of questionable and erroneous beliefs. He focused on three.
1) People have great pattern recognition machinery in their mind.
Unfortunately that means people often see patterns where there is, in fact, only randomness. A perfectly fair coin could land on heads ten times in succession and the odds of it happening an eleventh time would still be 50% but most people would think differently.
2) People test propositions by looking for evidence that supports them.
Positive reinforcement is much easier to find when you're actively looking for it. To test a proposition correctly you have to find both positive proof and a lack of negative disproof.
3) People are literally always of two minds about things.
We have a rational and an intuitive mind that battle against each other all the time. Intuition works better in situations where you have more data and/or experience, but people don't realise that.
Short-term marketers could and do take great advantage of any or all of those things and pull the wool over gullible eyes, but smart marketers who use them to help the customer feel more informed in their decisions and in control of their life will reap greater and longer-term rewards.