There are several questions about the Guild Reputation, one being the starting level to gain Guild Reputation and the other the minimum level of quests that can be done to earn Guild Reputation. When at level 83, what is the lowest level of quest that can contribute to Guild Reputation. Any quest that rewards experience to you will also reward guild experience. The amount of guild reputation earned is based on the amount of guild experience rewarded. Note that daily quests will also reward guild experience.
All guild reputation is gained as a factor of guild experience. Anything that grants guild experience will also grant guild faction, which means that winning a rated BG with your guild or completing specific guild achievements will reward faction as well as completing quests or killing instance bosses. As to Shaman, there are problems with the lowest tier of the enhancement talent tree. While elemental shaman do not want improved shield talent, they are basically required to take it to have a functioning PvP spec or a powerful PvE spec.