During my last transaction as a seller, the buyer asked me for my telephone number and telephoned me before we completed the deal. Initially I was a little put out of joint by this - I had a positive feedback history as a seller and I didn't want to give out my details.
That said, now I think it's a good way to go, especially given the large number of I got screwed threads.
Get their number, and give the seller (or trade partner) a call beforehand just for a friendly chat. At least then if the deal goes south you've got contact info outside of forum PMs plus anyone who is planning on screwing you won't give you that number to begin with.