[pault]

Definitely. I did see someone dump 1000 BTC on finex the other day though, and while it did cause a ~$1000 dip they were bought up in a few minutes. Like you say though, there's no way of knowing if the buyers were third parties or the seller rigging the order book (although I don't know how one could have much control over a transaction like that without having control of the exchange itself, but exchanges faking volume and manipulating the price is par for the course in bitcoin land).