Right now the biggest markets have over a thousand traders. One cynical way to gain a lot of mana is to just copy a big market. People will trade just trying to arbitrage between the two prices.

Anecdotally there seems often to be one largest "main" market, but if the copycat markets even get 20% of the unique traders, it incentivizes more copycatting.

Will Manifold do anything by market close to make this not rewarding?