You ( like him ) assume that because he see's something at a given point of time, that he can make decision on it. Yes he might see that there is an offer to se

You ( like him ) assume that because he see's something at a given point of time, that he can make decision on it. Yes he might see that there is an offer to sell at one exchange that is below the offer to buy at another exchange, but even if you knew that at some time X you can't place a trade at time X you need at least X + <some finite amount of time to get the trade to the correct market>. In that time lots of stuff can happen. That specific order might be filled or canceled by someone else who knew about it sooner or was quicker to act on it. So what do you do ? Do you wait to buy until you can sell ? What if I am in the same business and I send an order and then cancel it an extremely short period later, before that order could even propigate outside the market I placed it in ? I bet I could get you to buy my stock from me at a good price because you think you can turn it around and fence it really quickly. Guess what you might be taking a haircut on that one. And if I can get you to bite once I am sure I can get a computer to make you do it over and over and over again. This isn't made up people have done it [1] ( and gone to jail for it once they got caught ) 1.http://www.securitiestechnologymonitor.com/news/norwegian-day-traders-arrested-25971-1.html http://www.securitiestechnologymonitor.com/news/norwegian-da...