Before we get started, a word on Terms:
Spying is the divulging of sensitive or secret information to guilds or PCs who stand in opposition to the guild you got the information from.
Contrast this to information sharing, which happens between guilds or people who have the same general goals and often work together. Le'Megen T'Elysia and the Order of Gorethar often share information. Reavers and the OoG never do. When in doubt ask your sponsors.
An informant is someone who has ICly decided to pass information to a guild in exchange for something (wealth, power, not being killed, etc).
When I say "spying on X for Y" I mean, you are moving information from guild X to guild Y.
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From this point on, we will leave information sharing alone, and concentrate on spying. Everyone ready?
OK! There are four standards when dealing with spying in Avlis:
The Holy Order Standard
No PC may spy on a Holy Order for any other guild without permission from the Team, either via information from the forums or through ingame IC communications. This permission has never and likely will never be given. Your God has chosen you for His Holy Order... he will know if you leak information, and depending on the severity, He will punish or even evict you from the Guild. In other words, there will always be serious painful consequences if you spy on a Holy Order for some other group. If you wish to remain in a Holy Order, do not do this.
The Forum Info Standard
If you belong to more than one guild, information posted on private guild forums must be cleared through both guild sponsors before it can be PMed to another PC or moved from X's forum to Y's. As a courtesy, we also appreciate it if you tell the DM related to any plot info you leak, but it's not necessary. DM's have differing standards about how much info they will let you move from a guild's private forums. Some DMs may tell you to perform ingame actions before they will approve it. Some DMs may refuse altogether. Generally, we all frown on simple cut/paste spying.
The Ingame IC Leak Standard
~Receiving Intel~
If your PC is told something ICly, ingame, it is usually legitimate to write your own account of this information on your private guild forums. Likewise, it is perfectly legit to develop informants and gather information from them through ingame IC meetings. However, if somebody walks up to you with a bombshell stack of intel, please get approval from your Sponsor before posting it. Use discretion and common sense...
"Did you know that there's a thief guild that runs the Mikona Underground? It's true!" is not a bombshell. If somebody tells your PC that ingame, post it if you like.
"Did you know that Fergus Goodmane secretly runs the Mikona Underground?!" is a bombshell. Please ask before you post that.

~Being an Informant~
It is your responsibility as an informant to contact your guild sponsor before passing information ICly, ingame, from your guild to some other guild or PC. In almost all cases you will be told to simply carry on with any actions that are IC for your character, but the Team wants to know these things beforehand. If we discover that an informant is simply cutting and pasting forum information into the chatbar ingame, we will hold the player to the Forum Info standard and act accordingly. Be aware that informing on a guild can be incredibly dangerous for your PC, and that the Team is unlikely to take action to shield you from consequences beyond the standard prevention of grief play.
The Eavesdropping Standard
If you ICly overhear two member PCs of a guild to which you do not belong , telling secret information to each other, it's 100% legit. Give their guild sponsor a heads-up if you know it, or your own sponsor a quick note telling where you got the information, then use it as you like. Please see also: Avlis Policy on Sneaking Through Plot Doors.
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Registered Spies
The Team keeps a register of PCs who have blanket permission to spy on guild X for guild Y. This is an OOC distinction granted on a case-by-case basis, and kept by the Team in strict confidence. Once a PC is entered into the Register, spying requires only notification to both sponsors, not permission from them. If you find yourself needing to regularly spy on X for Y, it's more convenient on the Sponsors and the player to register as a spy. Again, courtesy is appreciated when dealing with sensitive plot information. Generally, the Team won't enter a PC into the register unless the player has already proven he can meet the Forum Info standard, and of course a DM can overrule this at his discretion.
Avlis is a world where fortunes often rise and fall based not on what your PC owns, but what he knows; spying is in integral part of the world. It happens constantly... entire guilds are built upon the networks of informants they have developed. These rules are designed to prevent the OOC strife and upset that can come from spying, and ensure that "double-crossing rotten bastard" remains something people say about your PC, and not about you.
-spool32