[jeffwass]

I mentioned this before, but one of my former colleagues quit to trade BTC and claimed he could account on some days for 10% of exchange volume.

No idea which exchange.

But his trading activity as far as I understand were on-average neutral (not net long or short). Though I think he also kept a bunch himself too.

So volume alone does not imply the exchange could absorb a large one-sided addition of sell orders without significant move in spot.

Also it's unclear if any of this volume is 'churning', by those with significant quantities of BTC happy to pay transaction fees to create a sense of false liquidity.

[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).