As a mobile marketplace, how does Offer Up provide value to shoppers? Sellers?

When people think of buying and selling things online locally, most think automatically of Craigslist, the classified ad marketplace that has dominated that business for the past two decades. But as the rest of the world has gone mobile, Craigslist has not. In fact, the familiar but cluttered collection of blue hyperlinks has changed very little over the years.
Enter OfferUp—a relatively new mobile app for buying and selling items that is taking the digital marketplace by storm. OfferUp is challenging not only Craigslist as the go-to platform by which individuals and businesses sell goods and services in local markets, it’s also starting to challenge the likes of eBay and even Amazon by flexing its muscles beyond local market boundaries. Unexpectedly, OfferUp now rivals the most popular social media apps in terms of time spent by users.