Of course he should be punished but the best lesson here is for bettors. Those who wager on "prediction markets": you are betting against people who have access to more information or can influence the outcome of the wager. Don't waste your money.
We would be much better off as society if bettors and gamblers actually learned from their lessons. Unfortunately that's not how it works.
Also, at least on Polymarket, beware of those who can influence the settlement of the wager, which may settle not in concordance with the actual outcome in reality.
https://www.reddit.com/r/CryptoCurrency/comments/1jki1lj/pol...
The real money is in providing liquidity if you don't have insider knowledge.
That's a very naive take of someone who never professionally traded. There are liquidity providing, market making trading strategies that work in absence of insider information.
This is true of all markets.
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That's sort of the point of prediction markets: they surface insider information by allowing people to profit off of it. The benefit is to people watching the prices, who can then use that information to make better decisions ahead of the answer being revealed to the public. It's not necessarily to market participants, who need to be aware of who else is trading the market and have a credible reason to believe they have better information.