There's no doubt that someone from behind can really manipulate the price and can suddenly pump the price to the extreme levels before suddenly cashing out and leave newbie traders wondering what had just happened. And its very fraudulent in my opinion, but we can't stop it because its been practice for so long. But as a precautions, its better to take and cash out if you see some good profits already and don't wait till the price declined and you have no choice by then but to sell wherein instead of getting 50% profits, you might end up in a loss.