A lot of times a large Buyer will place a large block size on the ask in hopes of scaring other nervous investors into selling their shares on the bid. A lot of times this works great for the buyer. Fear is a wonderful thing! How to tell if the ask size is fake is to hit the ask and see if they pull down the order? They apparently did pull down that 600K order when you hit the ask. Either the same person, or another large buyer came back in with 2 million more shares on the ask to scare more people out.
This tactic usually works very well for the large buyer, unless some Big Whale comes in and buys up all of their shares they have on the ask. Then it Backfires on them and they lose their shares! This is the risk they run they play this game. Usually they win though when the stock is in a down cycle. LOL
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