I'm not the developer working on the PoSA side of things, so for those wondering, the other Dev is working on it, its in the testing phase now.
Maybe also a catchall that nothing illegal may be bought or sold. The last thing you guys want is criminal charges that you helped set up another Silk Road, so the clearer you make it from the start that this is intended to not be that, the better.
But as long as we have your attention, I have some other suggestions. I read the whitepaper, but it has been a while, so I aoplogize in advanced if any of this is addressed there. Also I apologize if some of this is impossible due to the nature of anonymous wallets. But just some ideas.
* do not overlook the value of ratings - buyers should be able to rate their sellers and probably vice versa. I think this is the strongest assurance ebay buyers have. To me, this is more valuable than the trustless escrow. Trustless escrow is good, but the problem is if your run into a difficult person and you guys just can't agree, you both lose your escrow and you both end up losers, and I guess as a buyer it is some consolation knowing the seller lost money too, but it is still not a good situation
* there should be a history of how many successful transactions parties have
Also, I have some questions on the interface. How will the listings be organized? Will search work well? With all of this being decentralized, will there be a lot of lag bringing up listings?
I thought about ratings, and there is some simple ratings involved, such as number of failed/successful transactions with trustless escrow. The problem with ratings is they can so easily be manipulated. People will just pay for an item to themselves to give themselves a good rating. What use will ratings be then?
I was thinking therefore of leaving the ratings up to the listees in their posts. One could link to a third party trusted site that the community agrees upon in their listing post and people could view the ratings there. If anyone has an idea for a p2p style rating system that can not be abused I'm open. I could not think of anything on the initial concept for OneMarket. The entire team is always open to ideas though.