Comments - suffusion

Ah, you're already ahead of me.

I know you want to avoid having currency and I heartily support this. So whatever 'fee' the auction takes the form of has to be something else that modifies the behavior of the players putting things up for auction.

One thing I was thinking about was having NPC merchants who 'buy' those items that are overly prevalent. I know you already have decay, so depending on how that ends up playing out you might not need item sinks. But if you do, I can see NPCs who provide services (heals, MP regens, whatever) taking goods in trade.

At some point, you might consider having a "suggested bid" line for the auctioneer to set what they are interested in receiving. I think the bidding side of things is subject to more abuse than the auctioning side if there's no limit to the number of bids you can make, so you might consider limiting that as well.

Not allowing people to cancel auctions/bids would be one method of controlling storage issues, as you wouldn't be able to get the item back until the auction was over.