This is a great way to make money without spending any money on a buy-low, sell-high inventory. Let AH be your storage area and let others worry about paying for auctions.
1. Scan the auction house using auctioneer
2. Save two search settings in auctioneer:
a) Search Bids that profit over 50%
b) Search Buyouts that profit over 50%
3. In each category, run your search and sort by the most profit.
4. Look for easy to sell, high profit items. They meet this criteria:
- Blue or Purple
- Weapon, Armor or Special
- Under 40 level requirement or 60 level requirement (ie: ignoring items for lvl 41-59 is a strict policy of mine because not that many users will pay market price for non-twink stuff)
- High Profit PLUS low involvement on your part (ie: the profit is more than tripple)
- Items that are easy to sell and non-profession based (so NO recipes...etc)
5. In the trade chat, go 'WTS [item]' before you buy it.
6. When a person sends you a pst, asking how much, just say, 'how much do you want to pay'
7. If they offer you more than the item is worth by even 10g, just say OK and ask them to meet you.
8. Close the sale, and make sure they will meet you or accept COD (although COD takes too long).
9. Buy the item off AH and take it to them. They usually will pay you and you just quadroupled your gold.
10. If you get enough positive feedback from people but they don't have the money, just buy the item because you'll likely sell it anyway.
IF THE ITEM SELLS WHILE YOU ARE NEGOTIATING, DO NOT WORRY.
Tell them they waited too long and you sold it to someone else. Next time they will JUMP on the chance to buy from you.
Cheers!
A twist to this is if you are listing things on AH you can actually get people to buy your stuff and try to resell it to you. Simply go: wtb [item that you listed at an outrageous price] 200g Example: 1. Buy an item at 30g 2. List it on AH at 80g 3. Log, then relog as your alt 4. wtb [item] 124g Convince everyone that messages you that you WILL buy it if they meet you at a remote location. Then wait for the item to sell off AH as a greedy person attempts to dupe you. 
HAHA