How much of this is fixed if a person is only able to bet token amounts on each outcome? Let's get crazy and make it $20. A few crazy people might run Sybil attacks but it'll be a lot more limited and obvious. Not that I'm opposed to consigning all these gambling apps back to the fiery depths from which they came, but if you do want to preserve the ability of healthy people to have a little bit of fun, limiting the bet size has almost no effect on that while drastically reducing the damage. It seems like a good compromise, if anyone is looking for one of those.

PredictIt operated with $850 limits for years, and overall this seemed fine. Limits of various sizes might make sense depending on the subject, where the risk of penalty greater outweighs the potential profits.