I had a 'source' back around 2000/2001 who was one of the groundsmen at Princes park. I was amazed at some of the info he would get for me and how often it was spot on eg: The Hamill trade and the amount he was being offered by the Saints etc. Most of it was gathered by standing around outside the clubrooms talking to guys like Goughie etc.
AFL clubs are like suburban and country footy clubs - there are a lot of people who love to give the impression they are 'in the know' and a lot of stuff does get leaked.
Yep. Also I've found a good way to get information is to stand somewhere near the group of people gathered around the players race at VFL games or training as many of them obviously learned to whisper on a helicopter.