Have 2-3 trusted members to manage all trades.
even members can scam, even if they are 'trusted'. what if we are talking about +€200,-?
Ban all scammers by reporting them.
Who will know if they are realy scammers? fake reports are all over this place
Moderators will manage all trades.
How? how can moderatores will manage every trade?
Leave it as it is. trades at your own risk!
For me this is the best option, a tip from me? dont sell/buy anything from the internet