It is very simple to do. The trick is you send a ton of bids one after another on a cheap item. You will not be able to do this by hand, you will need a program *cough HappyAuction cough* What you need to do is to set up the program to spam bids (I set mine to be 5,000,000) and have it constantly outbid itself. This will force others out as your bids will be coming in to fast for them be able to bid and their bid will always be too low. Essentially what you end up with is the bid on the item and the item will be locked where it will show 0 bid and no buy out if anyone else is looking in the AH for it. When it is locked in a Zero state no one else can bid and you will have the low winning bid. The seller can not cancel the auction due to there being a bid on it. You essentially screw the person who low listed it with out a buy out. You in turn will win the item for dirt cheap and then just resell it. As long as no one else has bid on it, it will stay locked. If someone else has a bid all the need to do is enter a bid higher then your bid and it will unlock it.
Essentially you are exploiting their shitty Auction House Database by flooding it with entries. I have been using this for the last yea or so. Now that AH is going, I am giving out "my secret". Enjoy.
Edit: If you care about your account do not do this. Bans are not a guarantee, but the potential is there and the more you use it the higher the potential.