How do I access the Diablo 3 auction house?

Solution 1:

For anyone coming across this, the auction house (both gold and real money one) was removed from the game in 2014. https://us.battle.net/forums/en/d3/topic/9972208129

Solution 2:

There's a fairly simple step-by-step guide on Blizzard's site:

1. You will need to log into the auction house through Diablo 3 by signing into Diablo 3 and clicking Auction House from the left-hand side of the character selection screen. In the top-right corner of the auction house, you can access the real-money auction house.
2. To buy, in the buy tab, find something you want to buy using the search in the auction house, click on it and place a bid.
3. To sell, in the sell tab, select the item in your inventory and set bidding criteria.
4. Use the Auctions tab to view the status of your auctions.

View the Auction House FAQ for more.