Ok so this is a little trick I used to do for a while when I had nothing else to do.
1. Head over to the AH and buy all the "Shadow Crystal" on the AH for 50 silver or less. Even if it is 49s99c or 50s.
2. Make sure you have Gem Perfection. If not,
ALLY go to Valgarde (speak to Ounhulo) or Valiance Keep (speak to Alestros),
HORDE go to Warsong Hold (speak to Geba'li) or Vengeance Landing (speak to Carter Tiffens).
3. Cut you Shadow Crystals into any gem. Theres roughly a 50% chance to get a perfect gem. Now, sell all your gems you cut to a vendor. Normal gems sell for 50s, perfect gems for 1g. Do this in bulk for best results
4. Ask in trade WTB shadow crystal and buy in bulk too. Add regular miners to friends list and have them COD stuff to you.
5. /run SendChatMessage("WTB "..select(2,GetItemInfo(36926)).." <50s a piece. Accepting all COD's", "CHANNEL", nil, GetChannelName("Trade - City"))
This will say:
WTB [Shadow Crystal] <50s a piece. Accepting all COD's
in trade channel. Change the text as you please
6. ???
7. Profit!