no guarantee here, but if you use paypal as a payment method you are covered more than usually if you are a confirmed user. That means if someone decides to just take your money and not send your item, you can open a dispute in paypal and if they dont reply within X amount of time or the paypal case worker sees something wrong, you will get a refund. It happened to me a few times ( not here on head fi, on ebay actually ) but the paypal guys helped
buy ya, the steps?
-Create a topic in the correct forum for your item that you wish to sell or want to buy
-speak through private messages and exchange payment info
-send your money or item
-receive it and enjoy?