I play the Auction House more than I play Diablo 3. I’d say it’s 65%/35%. The reason for that is; I know what items are worth, and if you know what items are worth, you can profit, big time! As you can see in the image below, I purchased a good Natalya’s Embrace for 1,300,000 gold. This piece had recently been up on the AH, as it was 1d 11h left on the auction. So I purchased it right away, checked its value and sold it for 32,000,000 gold.
If you know what items are worth, then you will, more or less, see the opportunities when you can purchase items and sell them for more. If you don’t know what items are worth, or don’t have the time to look into that, you can check what similar items go for, better and slightly worse, to see if you can profit. This means you have to be quick, because there are nerds (me) lurking the AH all day just for these kinds of deals.
There is definitely luck (timing) involved in this. I never search for Natalya’s set pieces, simply because I don’t want it. But today it crossed my mind to search for one and by doing that, I just earned 27,000,000 gold.