They is no fools...
They will buy all you have to offer at their bid, and bring the ask down; but try to buy a sizable lot, that is what they do...
That is why I look at the BID/ASK RANGE of all MMS at Level II...
I Place ORDERS no bigger than the combination of the first two MM offering. Usually, you will see a big lot (50,000) as the demarcation point...
Gil...