I see where you're going, for sellers, within the app: Snap the pic, add some text, price and then a drop-down or "select" menu of all sites and urls where the seller wants it listed. Boom, boom, boom. Could also add the option of "only within 10 miles" or "20" etc.
The tricky part is the url link back to the app for the info (pic, price, etc.) - since most forums and seller domains have different criteria for uploading info - so it have to be a link only . . . aw heck, I'm rambling again - back to work.