The Real Money Auction House (aka RMAH) is finally live in Diablo 3 for the PC, and people seem to be listing everything they can in an attempt to make some extra money.
Be wary though, because the associated fees can take a hefty bite out of your profits.
Equipment Fees
The transaction fee for any piece of equipment is $1 USD, and an amount equivalent in other countries. This fee is only taken if the auction actually sells, but still that’s profit gone right off the top. If you have a low to mid level item that will only sell for $3, and you pay $1 just to sell the item, that’s 33% just to sell it.
Obviously the more you can get for your equipment, the less this fee will hurt your profits, so it’s a good idea to stay away from selling low value items in the RMAH. You would  be much better off
Commodities Fees
Commodities will charge a 15% flat transaction fee across the board, which will allow for much lower end auctions, but will greatly cut into the profits of higher end auctions.
Cash Out Fees
If you choose to keep your sales in your Battle.net account (which is the default) then there is no extra charge, however you can only use these funds for Blizzard purchases.
If you opt to cash out your money to Paypal (in which you need to setup your account, and make sure to select this when creating your auction) then there is another 15% cut from whatever is left from your sale.
