The orcs love bloodsports, everyone knows that. If you go deep enough into their lands, you will find their favorite entertainment is the Talbar, the arena.
In addition to the Thieves' Guilds, there is a hierarchy that all thieves are part of. Rank is based on skill, and can be raised or lowered at any time. The Queen of Thieves, the greatest living thief in the world, is the ruler. Guildmasters answer only to her, and she answers to no one at all.