Regular GMs can and do have access to certain things they can make appear. I know, I used to be a GM on another game. I made shit all the time. EQ GMs can move items, spawn items and change stuff in a limited fashion, somewhere there is a set of gm/dev/guide commands that shows you who gets to do what. BUT if you own the server, ie 99 jacktards, you can spawn in anything you wish at any time via the console command. So yeah they may not be in on part of it, but they have been caught way too many times taking money from RMTers and eliminating competition for those that pay, I would not log onto a 99 server for a million Kronos!
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In the case of Wow, the GMs know players were buying gold off other players, they send you a polite, "please don't RMT buy gold" but that's about it. It is not that they are in on it, they just know it is happening and they don't want to ban active players who are not actively exploiting/cheating. If wow and eq were smart they would allow players to buy gold/plat, oh wait EQ does.... Kronos...