The most common form of price manipulation is ramping, or...

The most common form of price manipulation is ramping, or artificially pushing the price up in order to sell larger volumes at a higher price. Signs of ramping include strong buying right at the close of trade at prices higher than during the day and big price jumps on low volume.
If a company has some very good news to announce and people close to the company want to buy more stock at good prices, another common form of manipulation is that of artificially forcing the price down, a sort of negative ramping. Signs of negative ramping are the exact mirror image of normal ramping, larger than necessary falls right on the close and big falls on small volume as sellers inexplicably fail to haggle or stand their ground.
This is particularly cruel to inexperienced market players, who fail to notice the warning signs and panic out of the stock, only to see it suddenly shoot up after spiralling downward. This practice has been referred to as 'shaking out the Woodies', a comparison of gullible investors to wood-ducks, which are notable for the ease with which they can be lined up and shot.