I'll preface this post by saying that your results will vary depending on your server's economy, but this method is a pretty sure fire way to make profit and takes little to no skill to accomplish.
As with many other people looking to get friends interested in WoW, I often find myself inviting friends to join my server.
More often than not, they want to start whatever type of character they prefer to play as their main, but I always make the suggestion that they make a DK as well and there's one very specific and simple reason why.
There is an extremely easy way to farm gold on a fresh DK which requires pretty much 0 effort and can bring in steady income depending on your server.
First, you'd obviously need the pre-reqs to be able to make a DK (level 55 on any server).
Second, you need to complete all the beginner DK quests and get them to the point where they can travel elsewhere in the world. Fortunately, as soon as this is done you will have access to all the flight paths and can head right to making cash.
Next, fly from the closest flight master to Tarren Mill (Horde) or Southshore (Alliance). After that you want to head straight south until you hit the shore.
From there you want to run along the shore to the west (see below)
Here you will be looking for and killing all the various Torn Fin Murlocs in the area (Torn Fin Tidehunter(s), Torn Fin Oracle(s), Torn Fin Coastrunner(s) and Torn Fin Muckdweller(s).
All of which have a ridiculously high drop rate for Thick-shelled clam(s). These babies drop Tangy Clam Meat as well as Iridescent Pearl(s).
The clam meat sells well on the AH due to it being a reagent for Goblin Deviled Clams, which is used by a lot of people to level cooking (in fact, it's used in a couple of guides for leveling cooking right here on MMOwned). I often have sold these or had friends selling them in stacks of 10 (they only stack to 10) for 25-30g per stack. The pearls will also sell well (though not to be confused with the Small Lustrous Pearls which also drop occasionally, just vendor those) as they are used for Runed Golden Rod(s) which are required for Enchanters.
By running the route along the western shore like I've shown in the picture above, you can get a ridiculous amount of Tangy Clam Meat as well as quite a few pearls with minimal effort spent (the murlocs all die in 1-2 hits max and wont be able to even hurt a new DK).
Killing the murlocs as fast as you can, you should be able to run this route over and over without having to stop. In the off chance that someone else is farming these, the Nagas along the east coast (Daggerspine Shorehunter(s), Daggerspine Shorestalker(s) and Daggerspine Screamer(s)) as well as the Snapjaw(s) along the ravine to the north also drop Tangy Clam Meat very reliably.
For best results, i've found it to be a good idea to have an addon such as Loot Filter to get rid of all the extra junk the murlocs drop.
If you do use loot filter, add the following to your DELETE list under the name tab (please note the enchant formula in here, you may not want to add that if you're missing it and want it on an enchanter for some reason)
Code:
Fish Oil
Shiny Fish Scales
Thick Murloc Scale
Melon Juice
Torn Fish Eye
Healing Potion
Lesser Mana Potion
[Formula: Enchant Gloves - Fishing]
That should filter out most of the junk that the murlocs will drop.
While this isn't the most amazing farming tactic, it's steady and reliable profit that can help any new DK get on their feet and it's highly unlikely you will have any competition for this area or on the AH. At one point I was the only person doing this for a few months and managed to inflate the prices of tangy clam meat to 65g per stack of 10!
I've tried to be as thorough as I can here, if you have any questions though feel free to ask in this thread. I hope this helps people looking for a different approach to gold farming, sorry in advance if this is a repost but I did search and found nothing similar before posting this.