The e-commerce site is flexing its muscles with large manufacturers, prohibiting them from setting their own Amazon prices if they sell elsewhere. Instead, they must wholesale to Amazon, which then sets prices and sells the products online. Some believe it’s a prelude to Amazon’s One Vendor, which will combine big brands and independent sellers to create a more uniform customer experience. One cellphone accessory-maker was recently banned from independent selling when it refused the terms. That company, PopSockets, decided to leave Amazon, and some believe big brands may follow.