We're aware of a number of so called 'second markets' for ethereum that have automagically sprung up in the last few days.
It's impossible to trade ether either during or post ether sale. The reason is as simple as it is obvious: if Alice tries to sell her wallet to Bob, what tells Bob that Alice has not kept a copy of her wallet somewhere? Nothing, its impossible to prove, and therefore it's impossible to safely trade ether pre-genesis.
Thank you to the many people who have reported this.