Yeah, that's exactly what I want to say. With nicehash you can't sell on your own and make more profit.
What mining pool are you using for ETH?
right now at ethermine.org - no outages till now and the rates look fine, tested also coinotron but they have higher payout limit and i usually try to take away my coins as fast as possible from pool to wallet
something additional to nicehash: a bit gambling you can do there too as e.g. right now BTC went bit down again so you can just keep your BTC you earn at nicehash and change later to $/EUR/whatever - so you can make bit more profit out of it by gambling with BTC exchange rate