What were the scammers doing exactly? I had quite a few buyers cancel trades and not pay but that was all. Im in Australia so really hope you do re-implement Paypal as its by far and away the easiest method of buying and selling bitcoins from here.
I am into sharetrading aswell and the broking firms here would only let you place a buy order for shares if you had at least an equivalent value of shares or cash in your account as collateral, which I think should be the case for bitcoin market too. If someone places a buy order and doesnt pay within 48 hours then Dustin can sell btc from the buyers account at the prevailing market rate in order to pay the seller.