I have about 20k in bars on my guilds connie too, from leveling Miner. but it is guild only, so I feel better because I trust my guild. It is sad that this happened, especially since not everyone has a guild connie in the area.
I have had this happen to me with Yew boards, when I was leveling fletcher. This was before I realized we had a guild only connie on the plot as well.
It would be nice if items could be tagged for an account so that nobody but your characters could buy them. This way, everyone could open up their connies and the problem would go away.
EDIT: How is it an unfair advantage if everyone can do it?