This seems too easy. How can offer such high returns?

Amazon is by far the largest online retailer in the US, grossing $107B in 2015. $37B of that is from Amazon Third-party Merchants. These merchants earn 23-155% returns on the physical products they sell through Amazon. By comparison, supermarkets earn much lower returns. Supermarkets' returns are so low because the goods they sell typically go from the manufacturer, through wholesalers, and finally to the supermarkets, with margins getting cut at each hop.

Amazon FBA Private Labelers get their products direct from manufacturers and retail directly to consumers through the Amazon platform, all without the overhead of maintaining a warehouse, or even shipping the products on their own. Amazon handles everything once the product is manufactured, from warehousing, to storage, and logistics. This enables Amazon FBA Private Labelers to capture most of the profits that supermarkets loose out on.

Given their uniquely large returns, it's easy to understand why Amazon FBA Private Labelers can afford to give away so much of their profits. They value growth most of all. With the funds from investors, they can focus on expanding their businesses as quickly as possible.