When inside a fief you can click on a target in the fief and spy on them obtaining all information. i.e gold, weapons and the last fief they were in prior to the one they are in now.
Spyings % chance for success is based on the amount of people in the fief. The more people the higher the chance of success.
I also though that your own clan could make it harder and easier to do, but I think that would kind of ruin the whole thing. If having 5 Greys in a village stoped you from spying what would be the point of it?
Also I haven't thought of what happens if you fail. Perhaps it could have 2 outcomes. Fail and escape and fail and get booted out of town.
If a clan has a capitol and they have it loaded with crafters and armies and so on, its up to them to police who stays in the fief and who doesn't. Its pretty easy for them to maintain control of who is and who isn't.
Poll