Mercari is a marketplace app with a rating of 4.7 stars and over 10 million users, facilitating the buying and selling of various items. Key features include quick item listing, instant payment options for sellers, promotional tools for visibility, and secure transactions with a rating and review system. Buyers can explore categories such as fashion, collectibles, electronics, kids' items, and luxury goods, with flexible payment options available. The app uses Mercari Prepaid Labels for streamlined shipping and offers international shopping from Japan.