Trading volume is not the important metric here. Trading volume is free to produce, order book depth/liquidity is not. The real value of an exchange is measured

Trading volume is not the important metric here. Trading volume is free to produce, order book depth/liquidity is not. The real value of an exchange is measured by how many it has of 1) dollars bidding on bitcoins and 2) bitcoins offered for dollars. This provides a cushion effect on the price of bitcoin, since large orders won't eat through as much of the order book and bring the price up/down. Trading volume is just people (allegedly) making trades. Liquidity can be easily tested by executing large orders, and seeing whether they will allow you to withdraw the proceeds.