Yea it is true. Although the more liquid the market, the harder it is.
If your a massive player and have a lot of size, it may be worth taking the other side to start a move (and lose a few points), wait for the move to be continued by other traders, to whom you then unleash your size into and beyond. Hopefully the result is that the lower average price you got out on would cover the loss on taking the other side to begin with, and certainly better than if you had just put them on the market with the current trend.
Thats the nice side of manipulation.
The bad side of manipulation is through false accounting, manipulation of statistics, fraud, Enron, corrupt analysts, etc
This manipulation can effect markets for minutes, hours, days, to unfold. Depends on the size of position.