Trading typically incurs slippage due to Bid/Ask spread. If not careful and liquidity is too low, you lose some going in and you lose some going out. IF liquidity is adequate, you should be able to at least buy at the ask, and sell at the bid. Many times you can do better if liquidity is there. IF liquidity is NOT there, my advice is to stay away. Look at the bid and asked sizes, as well as the Open Interest.