Selling App Startup Feedback

http://blastur.launchrock.com/ I wanted to gather some feedback about a startup idea I've had. The premise is that if you want to sell a used book or rollerblades, to find a buyer, you may have to wait months to connect with the right buyer or, you have to manage 15 different listings, one on each platform (FB, CL, offerup, letgo, ebay, etc.) My idea is to use api to blast this post to all these sites so you can post with one click and almost be guaranteed to connect with a buyer, quickly. Your candid opinions are welcomed.