PS: We could talk about prediction markets in general though.
Lets do that - I challenge that the very idea is basically nothing better than a ponzi scheme.
With zero regulation there is no reason for any party to "honestly" do anything (it is just a new way to relieve stupid people of their money).
Without me pointing to a particular case here, there's plentiful of examples where in regulated markets customers have been conned, schemes have sometimes been long in the making and are quite elaborate and big. If there would be more fraud with less regulation, I don't know.
I do think however that a businessman or company with integrity is able to conduct business with integrity no matter how they are regulated. So I disagree that with zero regulation there's no reason for any party to "honestly" do anything. Some businesses pride themselves with integrity and doing things in an ethical way. It seems however most companies don't as money is the driving factor, and then corners are cut.
We live very much in a trust based society. When you go to a restaurant and get a glass of water, you trust the waitress not to give you water you will die from. You trust the repository of your favourite linux distro not to contain any malware. Of course there are consequences in the real world to doing wrong things, if the waitress gave you poison in the water, she would probably be prosecuted for murderer. As such you could say society is "regulated". As for the linux distro, the malware would be a confidence blow among its users, so they have an incentive not to do anything like that.
The same exists with businesses in the crypto world. If you are concerned about running a business and having customers, and having integrity, then you run it honestly. If you're a crook, then you run it as a crook. Of course, it might be easier to get away with a fraud scheme online than in the real world. The face and identity of the fraudsters might not even be knows. But for the very sceptical observer, he should not be robbed, as there usually are signs something is up, well in advance before it goes titts up. Very obvious examples are MtGox and Pirateat42 in the bitcoin world. Lots of scams would be avoided if people were much more careful. However, it works like that most people are greedy, so then the fool and his money is easily parted.