You can do a couple things to lower the chance of being scammed.
1. Get a Official Middleman (OMM) or a trusted member of the community to act as a normal Middleman (i'd stick to OMM). Although, usually there are fees for their service.
2. Make sure the person you are buying for is trusted and has sold large quantities before. You can measure a persons trust on their post count, join date, donations and most importantly the value/amount of their vouches.
Good luck, hopefully this trade works out for you.