Zero posts and zero feedback is not such a big problem with BUYERS. At least as a seller, you can have some assurance by making sure you're paid before you ship the item.
If the payment goes into your PayPal bank account, and you have any doubts about the buyer, you can transfer the funds into another bank account. Don't ever keep a substantial balance in your PayPal bank account because they (PayPal or the people you transact with via PayPal) have been known to mess with it!
But assuming you've been paid and nobody will have further access to those funds (wait for the check to clear if it's a personal check, etc.), then there is no big risk in selling to an unknown newbie member.
But buying from a newbie SELLER with zero posts and zero feedback has caused a lot of our members grief! To help protect our members we now have a rule in place that restricts access to the Buy/Sell/Trade sub forums to only those members who have been registered from more than 30 days and have more than 50 posts.
While occasionally this rule serves as a bit of a hardship in the sense that we could have a member who has been registered for years, but yet has never posted much (and is still under 50 posts). He may want to sell his Sennheiser Orpheus system for an extremely fair price and has to turn to Audiogon instead. Although, in theory, this could happen, it rarely does. More often, we have the scammers who try to sell a pair of R10s at an EXTREMELY low price, but of course they don't own them.
So if you happen to see a for sale thread started by someone in any forum EXCEPT for the Buy/Sell/Trade sub forums, that means that the seller does not yet have access to those forums and is attempting to bypass the rules. It sometimes takes a while before such threads are noticed by a moderator or reported to us by other members. Please understand that if you see such a post and respond via PM and enter into a deal with such a member, you're doing so at your own risk (which I guess is always the case, but even more so in that instance).
Bottom line is that we do the best we can to keep our Buy/Sell/Trade forums free of scammers, but there is no way that we can guarantee any specific transaction and/or member that you choose to deal with.