I did a trade on USAM last year. The other party and I exchanged several emails, establishing trust and a way for us both to feel comfortable. We talked about packing, shipping, and insurance. Then we exchanged photos of our gear packed and labeled. Finally we exchanged receipts showing tracking numbers.
It wasn't as complicated as it sounds. I would propose something and he would either agree or suggest an alternative. It was all done over three days. Both of us were happy with the outcome.