^ I like that idea too. If we use paypal it should be as easy as a PM, see if payment was sent and go ship the flippin' thing.
Would we offer a list of acceptable practices? EG: If you're trying to sell something have it on hand ready to go (not at your friends that wont call you back in the next town), how to present items for sale (images - where/how to upload/share), acceptable ways to let the seller know you want an item so they can give you their payment info (prevent spaming someones PPR if they haven't answered someone back), preferred ways to send payment, preferred shipping avenues (or ways that will limit shipping costs per continent), Shipping cost standards/who absorbs shipping costs (to eliminate things like selling a game for $1 with $20 shipping ), acceptable time between payment and shipment, how to update your list/thread with a pending sale or sold indication, deleting PM's with personal info (name/address/telephone) to protect each other, etc...
Just throwing out ideas.