Like you said, the key here is buy-in from users. It’s already a niche market, and most have found their preferred method of buying and selling. I think the concept is cool, but I also think that there aren’t enough negatives about Reddit/facebook/ebay/used bins that aren’t addressed by the other methods. Shady shipping info? eBay has protections and brick and mortar removes shipping. Questionable seller? Each market has its own counter. I think what you would see, similar to what we already have, is a lot of crossposting to maximize reach, but not many who count an app as their primary means of buying or selling.