I have been scammed on Mercari twice within two months. The first time involved a seller not disclosing that the item was complete. It was sold as complete, but wasn't. My return was denied. Recently, I sold an item and the buyer, swapped out the item for the same, non-working item. Mercari allowed it. So basically, if you want to scam people, Mercari does not care. For those who are looking to sell, be wary. They will not listen to you and Mercari is no different than eBay. Find another place to sell.