I was very much intrigued by the Save or Die! Podcast Adventure #27 that came out yesterday. I made a comment to the good folks at Save or Die!:

I have played mostly Rogues/Thieves and I was interested in your take on Thieves Guilds.

In some of the campaigns I have played in, in smaller cities and towns the "guild" is sometimes non-existent or just a few thugs that have loosely banded together for mutual protection. Sometimes they are associated with a larger overall Guild that spans many towns and cities.

Some of the best thieves have an alternate identity in "normal" society. They can even work for or have friendly contacts among the authorities.
In general, in games where I DM, those that try to take up the trade w/o being a member of the Guild are eventually visited and given "an offer they can't refuse" to join the Guild. If they purposely try to run afoul of the local guild, they will be turned in to the local law enforcement or end up in floating in the sewers or something ;)

Not every game needs a fleshed-out Rogues Guild, but whatever one exists, unless it is a slipshod operation, the Guilds are very concerned with keeping a low profile, no matter how powerful they are. An exception may be openly corrupt cities or places where the Guild has grown more powerful tha[n] the official law enforcement.

It is really up to the DM, but these are some ways I have played such Guilds in the past. Just my two cents worth (actually, yours, as I just picked your pocket!)

See ya! :D

-Jeff
"DM Retro"

Click here to access the Save or Die! Podcast Adventure #27 Cyclops Smash!