Just because the rules are "clear", doesn't mean there isn't an element of scam.

For example: https://en.wikipedia.org/wiki/Dollar_auction

The Monty Hall problem has very simple rules, yet most people don't fully understand what's happening. That one even fools many professional mathematicians.

Even a spin machine in a casino has clear rules, with the house cut printed in large letters on the side. It's still a scam, carefully engineered to take advantage of every mental vulnerability that it can.