Choose Auction House in Diablo 3

You are supposed to decide the auction house you will use before you are able to buy and sell the loot you collected in Sanctuary. And there are two categories of auction houses diablo 3 provides, which can be switched at any time.
First, gold auction house, where items will be traded for in-game diablo 3 gold acquired in the process of adventures in diablo 3.
The other, real-money auction house, where players trade items for real currency.
For hardcore characters, they enter an exclusive gold auction house with "Hardcore-only". They don't use the gold auction house or the real-money auction house.
Every diablo 3 game region owns its own separate set of gold and real-money auction houses. And they are independent, which means that items listed on one region will not appear on another region.
The place you live determines the auction house you have access in. Generally, players are able to have access to the gold auction house in every game region, but if they want to access the real-money auction house, then you only allowed to enter your home game region.
Once you log in to diablo 3, the most suitable real-money auction house will be automatically determined for you.