ok i use this quite often i have earned alot of gold by doing this however sometimes gold can be lost.
1. Find an item in high quantity and demand on AH, find a day and time where people post items
2. start to post items undercutting competition by 1 or 2 gold
3 wait until people post items cheaper and undercut them
4. go as far as possible (you soon learn the max you can undercut so 1st few attempt you may lose gold), also keep records of how far people are prepared to undercut
5. when you are undercut by a decent amount Buy Everything < average price (remove all your auctions asap) best done with mats as there isnt a posting fee.
6. restock AH with items at average price on a weekend when the Buyers are out in force and profit
1st time i tried this i lost almost 1000 gold as i was undercutting and another person was using the same method as i was attempting only he was one step ahead and pulled out at the right time and made away making me lose 1k in profit.
after i realised its about timing and knowing when to cash in without gettiing too greedy.Now i can make 10k+ easily using this method