Poloniex pumps and dumps are done from the inside. Here's how I know.

There's a person (or bot) sitting in Poloniex and he is looking at all the account balances. When he sees that relatively small amounts are left for a certain coin, he pumps that coin. Once sufficiently many people buy in, he stops the pump. He knows exactly how many coins each person has on poloniex as he has full access to the entire Poloniex database. Then he dumps the coin, and waits until people sell at a loss.

I made two buys at Poloniex for recently dumped coins at significant positions. I sold the first coin after five days, and the second coin after seven days, both at a loss. The exact moment I exited my position (to the minute), both coins got pumped more than 70%.

Poloniex is a scam, and it should be reported to SEC.