Quote from swateckeThe majority of the QQ over RMAH comes down to the idea that people who have played through endless hours of content to get their items, and the prestige and sense of accomplishment that comes along with that, will be pissed off if they see someone sporting better gear than they have that has been purchased with RM on the AH.
For every item bought off the RMAH add a line of text under the item description and item stats that says " This item purchased on RMAH", or "RMAH item". I believe this will still enable people to purchase items on the RMAH but it will make other players that have earned their items the classic way feel more validated, and it will perhaps discourage gearing up solely by using the RMAH to purchase items.
While that would work, it would be even better if there was a right click on item command for each item(right click a item, and it shows the entire history of a item. Rather it was crafted/who crafted it, traded, bought in RMAH, exc).