If you are talking about manipulating small market cap coins, I believe the people behind the pump buy the coins they are going to pump in advance. This is only a small group of people who buy very cheap. Now, they have to have a huge following to whom they announce the pump. Next the pump starts, and the followers are starting to buy more and more. The price goes up quickly. As soon as the price has reached the desired level, the initiators dump their coins for huge profit. Most of the followers are left with small profit or nothing at all.