http://techcrunch.com/2013/11/04/dropbox-snatches-up-sold-th...
It's an interesting system to build, though, and there is money to be made. The very first version of my startup was something that was pretty much the same system, but we focused on offloading liquidation inventory. Some things that you will likely discover along the path
1. If you use eBay as your dataset, you are pretty much SOL. Their lack of rigorous moderation in terms of their image style guide makes computer vision really, really difficult to carry out. Using SIFT image features from the same exact images, I only got about a ~75% accuracy because eBay users tend to slap all types of random extra things onto their images. I can't imagine you'd have much success trying to use CV for identifying (with sufficient accuracy) consumer electronics in consumer supplied photos. I can't speak for Mechanical Turk... We wound up modifying our tech strategy such that we didn't need high accuracy in identifying other listings.
2. Product versions dramatically alter product value, but are just about impossible to figure out without being explicitly provided that data by the person holding the product.
3. Unless you own your own sales channel, you will be beholden to the marketplaces to offload the inventory in. In my case, we automated the process of selling on both eBay and Amazon. We were reading in data from multiple wholesalers (dropshippers), which had catalogs full of an arbitrary assortment of products... Which means we wound up listing weapons, sexual objects, etc. We got dinged pretty bad by eBay for these things (though, turns out batons sell really well on eBay). Eventually we pretty much got banned from both marketplaces for listing violations + bad fulfillment speed. We couldn't control the shipping speed of our dropshippers (we had no bargaining power), which I attribute to killing that section of the business.
As somebody who actually built the same system that you're describing (sans being an open marketplace, which actually makes it more difficult), I can say that you're in for a rough fight. Pretty epic watching an ebay store run itself, though...