why wouldnt you go through 3si PM's, they overlook/moderate those to
I don't know about David, but I cannot see private messages outside my own.
A lot of people will respond through PMs and not say anything in a thread. I do not list my PayPal address in a sales thread, you have to send me a PM. But just look at the member's profile, and on the right sidebar you will see group membership (right above "recent visitors"). If they don't have a "group membership" box, they are not a verified seller. Make sure it says "verified seller" in the group membership box.
If a member started a sales thread, they are a verified seller. It's when people contact you out of nowhere trying to sell you stuff, that's when you have a be careful.
Most of my transactions happen through PMs after I start a sales thread... it helps with not cluttering up a thread.