Basically what they do they sell let say at 17 and create a...

Basically what they do they sell let say at 17 and create a short-term panic and they will buy it back at 16.5 so half a cent profit. E.G. if the sell 1000000 at 17 and buy back at 16.5, they made $5K which is not bad for a day. Normally, there are group of brokers (Client advisers)which they do that simultaneously. Even those 3, 30, 300 etc which was mentioned in previous posts could be basically codes among them :) You can check this by looking at the course of Sales and see if there are any connections between those small trades and sudden large sells.