I usually send two PM's and one forum message. The first PM says I want your thing and will PM you again soon. Then I post a "PM sent" inside the thread. Then I send a longer PM requesting payment info or asking simple to answer questions while providing my contact info and shipping address.
This has covered most of my situations but if the forum is going down or PM's are full I guess I would shoot an email explaining my situation.
Summaron 35/3.5, Jupiter J8 50/2, Industar 61LD 55/2.8,
Contax G2, Planar 45/2.0, Sonnar 90/2.8