Common problems/essential things/suggestions:
1-Doing this is hard and will take time and will most probably come with bugs such as duplicating items.
2-If you lose bid,you HAVE to get your gold back,otherwise,when bidding on a lvl200+ item,you will most probably lose 50m+ gold.
3-Losing won item within 24 hours and item goes back to owner has to give back gold to bidder otherwise it's not fair for busy players with jobs/schools.Which leads to another problem of over priced bidding to prevent other players from buying it,then log out for 24 hours to get gold back.Sounds more like bullying

4-Each player can only put 1 item at a time in auction house.
5-Seller loses a percentage of total gold of final price of the sold item (that goes to auction house

6-Limited time chosen by seller (3 hours - 6 - 10 - 24) which may or may not change the percentage of money that goes to auction house (from number 5)
7-Double click to avoid complains such as: I clicked the sell now button by accident when putting the price. OR I accidentally sold for 100k instead of 1m (missed one zero)
That's all i can think of for now,but you get the point
