Sorry if this was mentioned somewhere but I haven't seen it. This isn't really an exploit more so just a really scummy tip.
Players who teleport into Dalaran above Karazhan aren't in the sanctuary. The landing pad and part of the building leading into Dal aren't protected by sanctuary and are under normal pvp flag rules.
I've been using this to farm bloody coins. The real kicker is dying up there means you can't reach your body. Currently you have to spirit res at the GY below. This leaves you with res sickness.
You can camp the pad above for easy kills. If there's too much competition for killing blows you can move the GY and camp res sickness players instead.
(I know there's a guide on bloody coin farm but it involves win trading. This is just easy HKs, use it however you like.)