Amazon is one of the biggest direct-to-consumer marketplaces on the planet. And not just of its own goods and services: though the company operates huge warehouses all over the world, it also lets smaller companies sell harder-to-find items on its marketplace, including individual sellers of new and used items. But with a relatively wide-open policy towards third party sellers, a few with less than noble intentions are sure to slip through the cracks. Here’s how to spot them.