I have done a lot of buying and selling here including a few guns. I have only had 2 bad experiences. One was sending payments for a part, receiving the part, then being told payment was never recieved on their end, sent payment a second time, was told it was not recieved, both were western union money orders, both were cashed.
The other was some mags sent to the address on my paypal and not the address I asked for them to be sent to. Numerous PM's went unanswered. I eventually got the mags 6 months later. Never did get a reply.
Those 2 out of probably 100 transactions. If its an established member of the forum, you should be fine.