The RMAH will become a place to only sell gold IF no items that are worth more than 4.5$ drop. Once items are worth more than 4.5$, they're worth listing on the RMAH. 4.5$ or less, and you're better off selling them on the GAH and then selling the gold on the RMAH. This is all due to the 1.25$ fee for items and 15% fee for gold on the RMAH, and 15% overall fee on the GAH.
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Can anyone show me how to figure out this 4.5$ line? I knew the 15% fee for gold on RMAH and 15% overall fee on GAH, as well as the flat 1.25$ fee for items on RMAH. But I did a terrible work in maths during school time. :P