Quote from zdreg:
where are these"hidden pools" of liquidity which offer the best price. what makes you think they deal with anything less than 5000 share lots.
Some or all of the major ECNs provide hidden order types. These are a very large source of hidden liquidity. Hidden orders can generally be sized as small as a one single share odd-lot, or 100 shares, or anything smaller or larger.
Another source of hidden liquidity consists of black-box trading algorithms, which are waiting for the public display of a contra-side price within a desired target range, so that the black box will respond by immediately hitting that displayed price as soon as it is flashed.
Another source of hidden liquidity is the "discretionary" order type supported by many ECNs and I think even by IB and some other brokers. Go read about how discretionary orders work, and you will see that these are a source of hidden liquidity.
Other pools of hidden liquidity are those specifically mentioned by zdreq, but my point is that those are only part of the picture.
IB's own proprietary orders are also a pool of hidden liquidity, with which customers trade whenever they get an execution with IB.
If IB trades with its customer at the best price displayed in the market, this disadvantages the customer and benefits IB, because the best displayed price is inferior to the best price, which might be hidden or might be displayed. The difference between the best displayed price, and the best price (displayed or hidden), is value gained by IB at the customer's expense.
I don't think IB does this out of dishonesty. I think that IB simply doesn't realize that its order routing logic is suboptimal in this regard. I am sure that if customers show that they care about this issue, IB will do the right thing and make the appropriate changes. IB's business model has always been to make money by helping its customers to make money, not by deliberately stealing from customers.
But HoundDogOne's approach of extreme disrespect and accusations of dishonesty will not establish the type of communication needed in order to effect constructive change.