Well heres what i do for extra gold, when im not doing other things.
Go to the AH and search it for bars. Scroll down the bars looking for auction prices that are alot lower then the buyout prices. usually people wont be paying attention and not up the bid price, for example they put buyout for 2g but the bid price is only 30s.
You can do this for anything, most comon in bars on my server, but i usually type in bars, ore, shards, and dust.
usually works, just resell for the price they were selling it for. They feel like an idiot and you get some extra cash.
I usually can make anywere from 2-10g doing this real quick, just like 15min to bid on all them, go do something else and then comeback and makeshure no one is outbidding you, repeat till you win the auction.
Edit: also when selling it you can try and sell it for ( useing my example from above ) 1g 99s instead of 2g, people just look at the g part ususally and buy it befor they buy your compeditors because they think its cheaper.
Minimish - "
a nice way to do this is like volund said buy rare items or expensive items and resell em, but do this just before maintenace that way u cant be outbid its a great way of making money

"
Just a thing i found helps me with gold, hope it helps you
-thebest