by Thunderstruck » Tue Jan 05, 2016 9:58 pm
The auction house cut is 15% which isn't terrible. You can also see if anyone you trust would make an even trade for the opposite alliance gold. Or you can buy things that sell for the same amount on both sides, transfer them over and sell them on the regular auction house to avoid the 15% cut.
It's not bannable. People do it all the time, that's how you see opposite faction recipes on the auction house.
To do it, remember that you do need a 2nd account since you cannot purchase your own items from the same account.