Didn't know whether to put this in Guides or Scams so mods feel free to move should you think it's the wrong section.
Anyway....
Using a few basic facts you can 'scam' your way to a lot of gold (though it's not really a scam either!).
Fact: Most people use the Auctioneer addon.
Fact: Auctioneer displays a percentage of normal price value.
Now assume you have an okay epic (not great and not really much value to anyone). An example would be Numlaks Supernumery Sticker (a tanking dagger?!). On my server it sells for about 500G-650G normally.
I rolled greed on one and won so as it was no use to me I posted it on the AH to no avail. So I thought about it.
So this is the guide part:
1. Post the item for a stupid amount of gold on the AH and leave it for a day (important that you leave it for a day). I choose values about 3734G (make it a random amount not a nice round number as people assume this is an addon entered value)
2. Cancel auction and repost it for the 'normal' price + a few hundered extra gold. (900G for example. Make this figure nice and round)
3. Now because you've posted it as a vastly reduced price Auctioneer will display it as a blue 24% cost (or what ever the % is for the item you've listed).
4. Some AH player will buy it and relist it for your original listing price. It won't sell for stupid price, the buyer will keep relisting it (I've watched my dagger be relisted 4 times now, getting less and less. It's now less then he paid for it!)
5. ?????
6. (Extra) Profit
I generally make about 300-400G extra then the items worth from doing this.