Why would someone buy 10,000 shares then immediately sell 10,000 shares?

[raszorz]

Why would someone buy 10,000 shares then immediately sell 10,000 shares?

print example:

10:30:00 Bot 10,000
10:30:00 Sold 10,000

^-- the seconds
are the same for both.



I see this frequently. Sometimes someone will buy multiple sets of 10,000 orders then someone (else?) sells a few 10,000.


I've been assuming that they're testing the market depth but any response with conclusive reasons or from someone that has actually done this would help.

Thanks.

 

[j_medved]

how are you determining that one is a buy and another is a sell?

 

[raszorz]

It would be a buy at the offer or a sell at the bid. Occationally it may print in between the bid/offer...

 

[speedy]

Many times its because they print it twice (albeit, only one trade) because its in the third market. Doesn't necessarily mean that its a buy and a sell by the same person.