So. I saw a bunch of people in trade selling level 25 guilds for some odd reason. It seemed a bit strange to me that this has been happening often. I went to look up one of the guilds these people were selling and I found this:
http://us.battle.net/wow/en/guild/da...a_Prodigy/news (scroll all the way down, click "load more", and scroll a bit further downwards)
If you look at the news tab, you'll see that the guild went from level 1-25 in less than a day. It's not there now, but I saw multiple level 4 human characters under the "Top Weekly Contributions" with over 100m guild exp.
It seems as if they are exploiting something?