[Interview With a Goldseller]

An oldie (2010) but a goodie, and still relevant to many games today:

Despite the vitriol with which most MMORPG players attack goldfarmers and the whole concept of RMT, the fact is that this market has existed since the birth of the MMO itself and in many ways is actually -enabled- by many of the conventions that oldschool players have held dear since day one (such as monthly fees).