I know that the posting fee are needed so that people won't cancel their auction halfway just like that. But that's also the reason why people is still spamming on the trade chat, because they're afraid that their items wont sell and they have to lose the posting fee. I would like to suggest that people will still lose their posting fee if they cancel their auction halfway but will get full refund of their posting fee if they hold their auction until the end of the auction period they have chosen earlier even if no one bid on their posted item.
The problem with this is that there is no disincentive for people who would post unrealistic auctions. If there's no fee for items that don't sell, people will try to put 30k cr as the min bid for all of their 5* mats. Then the next day, they'd just try at 29k and so on and so on.
With the fee in place, people are encouraged to keep the starting bid low. It sucks if you have a reasonable price on your item and no one bids, but I'm not sure how else they could do it.
Also, if you really want to have no listing fee, I assume you can put up auctions with 0cr as the starting bid price.