Well, this is a touchy subject AFAICS. On one hand, if you are a good RPer, then there would, in theory, be no problem with having multiple alts in multiple guilds.
However, in reality, this still is a problem even for the best RPer: you can only act with one char at a time.
Anyway, the worse problem is spying. The way to spy using alts is cheating IMNSHO, unless you notify both guilds in advance. Why? Because it is abuse of the limitations of the game (freedom to have alts, in this case) for purposes not intended. The proper way to do it would be to RP it all. In this case, you would be in yout original guild and RP your way into the target guild. Obviously this takes a trmendous amunt of RP quality on the target side, so this will most likely not be feasible. Still, the other way is not acceptable IMO. It is possible to find out, BTW. Takes some time, but is possible.
Edit: If this indeed is about one char being in >1 guild, then this is not possible by game mechanics, but could be acceptable from an RP POV. Non official \"guilds\" would be the only way around it and they are very much like secret guilds, anyway, so the difference would be minimal. Same restrictions as above apply to behaviour, though.
