You're right. IB's Ideal pro acts in the capacity of an agent. They simply pass it on. No obligation on the part of the bank(s) (liquidity provider) to accept/execute the order. Especially if you use a limit order. A market order has the highest probability of being filled. But has the lowest probability of a "good" fill. I've had a few Buy Limit orders that weren't executed even though they were placed 2 pips above the market. But the market was moving fast those days and were at breakout levels.
