One trader cannot set the nbt/cny price without also setting the nbt/btc price. The btc/cny market has much more volume than either of those markets, so if we assume the nbt/btc price is fixed by arbitrage with Polo, and btc/cny is fixed by arbitrage with Bter, the nbt/cny must be fixed. If one trader tries to move the price they will get hit continuously by arbitrage with Bter’s btc/cny and Polo or Nulagoon’s nbt/btc.