If you like to get more people to play diabo 3 here is how you get more people to play diablo 3.
Only for non season.
Start your own auction house with 10 friends to join have it like on neverwinter game. Guest can not see what your selling or buying, they need to join that person's group to see the items for sell or buy. Limit on how many items you can sell at a time like 10 items. Limit of how many auction house groups to join like up to 5 auction houses to join.
I would have reserve price on each items so people can not jack up the fake prices. The price will be like selling to vendors selling the items.