I for one do not post in the for sale thread that I have sent a PM. I only PM the seller. Knowing that someone has replied in the thread with PM has been used to scam people.
Details of scam:
http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/1128683-3-2l-twin-plugged-heads-w-cam-towers.html
I also figure seller can sell to whoever they prefer, I go with first to respond and pay.
john