As a rule of thumb, a member with a lot of posts (eg 500+) more more likely to be trustworthy than a member with 20 posts. It is still no guarantee though a good indicator of whether a seller or buyer needs to be treated with more caution.
Some questions to ask in a transaction.
1. - Can you organise payment on receipt of goods or use a payment system that allows reverse charges or is a truehand?
2. - Courier Beware. Some couriers (or fake couriers) pickup goods and won't reveal to where it was delivered - should you use the buyers courier company before you receive payment? Other couriers are non-existant in delivering something to you, should you pay-up before receiving?
(I realise that this is ambiguous, hence refer to 1.)
3. What do you know about the seller, mobiles and email addresses can be discarded but a street address is harder (though not impossible) to falsify.
While Bicycles Network Australia will pass on details it has in the case of a fraud or suspected fraud, this may not always be sufficient to track down an individual and start legal proceedings.