It's not refunded. I put up a few less popular 2 star mats for only 100 credits each and they didn't sell, so that was 50 credits down the hole just for putting it up for auction. the listing cost seems to way too expensive, IMO.

It's an auction house deposit. It's done in real life too. It ensures the auctioneers can get some profit even if the items don't sell, and prevents people from re-listing the same thing forever at no risk-- because real-life auctioneers have limited storage space and limited labor/time to sell the items in question. It allows them to cover opportunity costs and negate their own risks, else they'd go out of business.

It's done in games so you have to stop and think twice about whether it's worthwhile to list your item, and punish people for spam-listing overpriced garbage hoping that at least ONE of them will sell.

The list price appears to be 10% of the starting bid (with a minimum of 100 crowns). It's lost if the auction fails, and it's refunded if the auction succeeds (they make their livings off the 10% cut instead). Still, 10% seems a little much... I'm more accustomed to something more along the lines of 5% in games.

From what I saw, the list price is 10% after a certain level, depending on the item/mats. There is clearly a minimum list price. I put up a 2 star material for 100 credits, but the list price was 50 credits. That doesn't make a lot of sense to me. And putting multiple materials in the same auction increases the minumum. But I haven't thoroughly tested that.