The purpose of an Official MiddleMan is to safely exchange items from party A to party B. Such as, if party A is selling a RuneScape Account and party B is buying it, an OMM would exchange the account and cash safely between the others by, as the name calls from, being in the middle to take the account and cash and give the items to the respective party.
Haha. I was thinking the same thing once I noticed you had posted above me. I checked to see that no one was viewing the thread and they weren't. I'm sorry SuF. *pats back*