I've bought and sold on here for a while and have had good experiences so far. Few tips:
1. Try and buy local if you can so you can pick up and inspect b4 you hand cash over
2. Failing that if you need to purchase from interstate, check the users background, things like how long have they been a member, trader ratings, check out their posts under user options, see if they are good mates with longstanding members or have attended public meets etc...
3. Phone the seller, ask questions, possibly chat via msn as well so you get a feel whether the buyer is genuine or not
4. Ask for pics
5. Be wary of newbies that have signed up the same day with 1 post to their name trying to flog cheap parts off
6. Rely on your gut instinct, if its too good to be true it normally is.
I actually had a really good experience few weeks back, actually persuaded the seller to send me the items before payment was made due to suspect circumstances. All worked out well in the end
GL!