While there are plenty of marks for some thievery in the city itself - particularly from merchants, or petty theft from travelling adventurers - it doesn't really seem plausible that a whole industry could operate just within the city itself.
Profitable, surely, but too dangerous for day to day thievery. Third, and perhaps most importantly, a large portion of Greyhawk's population are adventurers. Second, the thieves own many front operations and outright legitimate businesses - so their potential targets are drastically cut down. This is problematical for several reasons. The problem I have is that most, if not all, of their activities take place in Greyhawk itself. However, I don't think that they take it *nearly* far enough, given the magical nature of the world, especially in 3e. Greyhawk is described as a free city, secretly run by its Thieves' Guild. I don't know much about Gygax's original vision for the city, so it doesn't enter into my idea here. Okay, here I am speaking of the version of Greyhawk as published by TSR and WotC and in its current form (though ignore the stupid ass 'From the Ashes' world war as much as humanly possible).
