I don't see why USD trades won't be mediated. Is there for a reason for this? I know it probably won't be totally risk free, but I'd at least feel a lot more safe trading while a mediator is helping.
E.g. with paypal, the seller gives the item in question to the trade mediator, who tells the buyer that he has received x item(s). THen, buyer pays via let's say paypal, and sends a confirmation e-mail to the seller that he has received the item, and will not chargeback transaction #12345678. Then the seller confirms this with the trade mediator, who then gives the item to the buyer. This way the seller cannot scam because the buyer will receive the item, and the buyer cannot scam by not paying / charging back.
Also it shouldn't take up that much time in case there are too many requests.