The Requirements are:
-Must have 800+ posts
-Must have a good reputation in the whole forum especially in the Marketplace.
-Must be well known as a legitimate trader with tons of vouches.
-Must have a vast understanding on how to do trades of each and every games/items.
-Must be in the site for at least 4-6 months
-Must not have a bad or suspicious history on MPGH
Once you complete the requirements, you can apply if a Middleman Recruitment thread is opened.