It can keep the same look as now, except include bidding and a buy now price, charge something like a 5% or 10% listing fee that gets deducted from the sale price or if it doesn't sell, gets deducted from the bank, force a person to retain the value until there is an initial bid.
It's not a huge change, but it would do a bit towards the inflation issue, mainly with RM packs and Awake Pills, as well as help keep the market less cluttered from items hanging around on there for a long time.