Till today the real-money auction house, AKA RMAH, are all revealed in EU and US server of Diablo 3. Known as one of the top features of D3, a lot of players are looking forward to this, who would like to try making benefits from RMAH. It won't be easy. But worth try.
It's important to get well prepared before entering the real-money auction house. For example, to know what items are rare, know the possibility of being rare of an item, or what items worth most. It would sound easy for other games. But in Diablo 3, as we all know, quality of items are random, either dropped items or crafted items. Thus, to do some research will make it easier. Remember useful items you saw. Unless you know well of item's profits, it would be very difficult for you to master the real-money auction house.
Meanwhile keep a sharp eye on the market. Note the price of common items and rare items, how the price changed. If you have a good understanding of items in the RMAH market, you'd be able to keep up with the profitable rates. You need to look at the market for every three hours.
The next thing you can do is to farm as much as you can. Searching for rare mobs and boss, which may drop rare items. Many times it's not necessary to pick up every items – choose ones will sell good price in the real-money auction house, or on gold as well. A good predication of the trend will lead you to a good profit. Even a white item has the possibility to be expensive when a character level up. Many a time's prediction can help you to figure out whether the item will be worth or not in future. If you have a hint of some items, store them. At times they will make profits.
Since Blizzard has brought PayPal into the real-money auction house, we can make real money from a game. I believe this is the reason why many people love Diablo 3, though it's not easy to reach their goal of making money based on the large amount of fees. As many plan to do so to hit level cap first and make profit selling items found in Inferno level, you can start by yourself. Buy good gears so you can survive and beat Inferno.
When selling or buying items on the real-money auction house, there is a common note of safety on the case of online shopping: beware of the in-game prompts you received that may not directly lead you to the appropriate web page to add an Authenticator or attach a PayPal account.
If it's the first time of selling items on real-money auction house, you need to attach a PayPal account or add an Authenticator to your battle.net account to use the RMAH. It based on what you prefer for your real-money auction house trade. To use the Battle.net Balance for trading, you need a physical Battle.net Authenticator or Battle.net Mobile Authenticator. To use PayPal you need to set up a Battle.net SMS protect on your Battle.net account first, then you can use PayPal with the real-money auction house.
For more information about the RMAH, you can check on the Real-money Auction House Guide and FAQ on Diablo 3 official site.