If a user receives an item that is not as described, they should first carefully review the listing details and compare them with the received item. This includes checking the photos, descriptions, and any specifications provided by the seller. If the item clearly does not match the listing, the next step is to communicate with the seller through the Mercari app. It is important to remain polite and factual in the communication, providing evidence such as photographs if necessary. If a resolution cannot be reached directly with the seller, the user can initiate a return through the app. This process typically involves selecting the item in question and choosing the option to report that it is not as described. Mercari generally provides guidelines for returns and may require the user to ship the item back to the seller. For detailed instructions or specific inquiries, it may be useful to visit the relevant section of the Mercari website for the most accurate and current information on handling such situations.