Completed sales have price information about the items sold. Our statistics from collectibles websites show the most common search is by visitors trying to figure out what their item is worth.
A completed sale, with pictures, a description, and some information from the sale will be a big help for this.
It also removes a major annoyance I had with selling unique items. It really annoyed me to do all the photo and writing work and then throw it away as soon as the auction ended. That feels like a treadmill and I want no part of it. By keeping completed item information on the site it adds to content, provides value for visitors and may even generate some income from contextual advertising.
