&gt; Be clear what you are saying. They are &quot;manipulating the price at other exchanges&quot; by changing the prices they themselves set on their own inventory.<p>Which will be sold instantly, as they have &#x27;discovered&#x27; the price on the other exchanges were lower than where the initial order went to, bought that, and then instantly, give or take a few milliseconds, resell.<p>It is not price discovery, it is price manipulation.  HFTs have no inventory, they are perfectly lean, they throw hot potatoes across different exchanges.<p>Not that this is not interesting technology.  It is, but it is also manipulative.<p>I exclude prop trading from the above, obviously, because it is different, and does hold inventory.