This technically isn't an exploit, but it is an easy way to get Astral Diamonds.
Make a GWF. Level him to 7. Wait for the Skirmish event and queue for skirmishes until it's over. Delete the character and start again.
How this works:
1. 1000 AD per Skirmish and you can easy do 4 each skirmish event.
2. The queue system tries to put one of each class into each skirmish/dungeon and there aren't many GWFs, so the queue times for them are almost instant.